Chapter 6 Basics of SQL Language
6.1 The SQL language
The acronym SQL stands for Structured Query Language. It is the most used language worldwide for relational database management systems. Whenever you interact with a database in your daily life (for example, any time you browse an online shopping website, or any time you look up something on StackOverflow!), there’s a good chance it was written in SQL.
SQL is a language that is used and understood by different database management systems, such as Oracle, PostgreSQL, MySQL, or SQLite. While all these programs share many similarities, which one of these you’ll end up using depends on the specifics of what you need it for. For the purposes of this class, we’ll be using SQLite. SQLite provides all the core functionalities you’ll need to get familiar with databases while being lightweight in terms of setup (easy to install and to configure). At the end of this chapter, we’ll talk about why you may want to make a different choice in the future, but for now we’ll stick with SQLite.
Each database management program uses a slightly different dialect of SQL. The language is the same, but there may be some slight differences in the syntax between different programs. I’ll point out throughout the chapter when we encounter syntax that is specific to the SQLite dialect.
6.2 Writing SQL queries
The nice thing about SQL is that it sounds a lot like human language. An SQL statement, or query, always begins with a verb that describes the action we want to do. A semicolon at the end of the query lets SQL know that we are done talking. For example:
## dragon_id
## 1 D1
## 2 D10
## 3 D100
## 4 D101
## 5 D102
## 6 D103
## 7 D104
## 8 D105
## 9 D106
## 10 D107
## 11 D108
## 12 D109
## 13 D11
## 14 D110
## 15 D111
## 16 D112
## 17 D113
## 18 D114
## 19 D115
## 20 D116
## 21 D117
## 22 D118
## 23 D119
## 24 D12
## 25 D120
## 26 D121
## 27 D122
## 28 D123
## 29 D124
## 30 D125
## 31 D126
## 32 D127
## 33 D128
## 34 D129
## 35 D13
## 36 D130
## 37 D131
## 38 D132
## 39 D133
## 40 D134
## 41 D135
## 42 D136
## 43 D137
## 44 D138
## 45 D139
## 46 D14
## 47 D140
## 48 D141
## 49 D142
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## 51 D144
## 52 D145
## 53 D146
## 54 D147
## 55 D148
## 56 D149
## 57 D15
## 58 D150
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## 60 D152
## 61 D153
## 62 D154
## 63 D155
## 64 D156
## 65 D157
## 66 D158
## 67 D159
## 68 D16
## 69 D160
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## 79 D17
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## 103 D191
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## 106 D194
## 107 D195
## 108 D196
## 109 D197
## 110 D198
## 111 D199
## 112 D2
## 113 D20
## 114 D200
## 115 D201
## 116 D202
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## 135 D22
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## 140 D224
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## 142 D226
## 143 D227
## 144 D228
## 145 D229
## 146 D23
## 147 D230
## 148 D231
## 149 D232
## 150 D233
## 151 D234
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## 156 D239
## 157 D24
## 158 D240
## 159 D241
## 160 D242
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## 162 D244
## 163 D245
## 164 D246
## 165 D247
## 166 D248
## 167 D249
## 168 D25
## 169 D250
## 170 D251
## 171 D252
## 172 D253
## 173 D254
## 174 D255
## 175 D256
## 176 D257
## 177 D258
## 178 D259
## 179 D26
## 180 D260
## 181 D261
## 182 D262
## 183 D263
## 184 D264
## 185 D265
## 186 D266
## 187 D267
## 188 D268
## 189 D269
## 190 D27
## 191 D270
## 192 D271
## 193 D272
## 194 D273
## 195 D274
## 196 D275
## 197 D276
## 198 D277
## 199 D278
## 200 D279
## 201 D28
## 202 D280
## 203 D281
## 204 D282
## 205 D283
## 206 D284
## 207 D285
## 208 D286
## 209 D287
## 210 D288
## 211 D289
## 212 D29
## 213 D290
## 214 D291
## 215 D292
## 216 D293
## 217 D294
## 218 D295
## 219 D296
## 220 D297
## 221 D298
## 222 D299
## 223 D3
## 224 D30
## 225 D300
## 226 D301
## 227 D302
## 228 D303
## 229 D304
## 230 D305
## 231 D306
## 232 D307
## 233 D308
## 234 D309
## 235 D31
## 236 D310
## 237 D311
## 238 D312
## 239 D313
## 240 D314
## 241 D315
## 242 D316
## 243 D317
## 244 D318
## 245 D319
## 246 D32
## 247 D320
## 248 D321
## 249 D322
## 250 D323
## 251 D324
## 252 D325
## 253 D326
## 254 D327
## 255 D328
## 256 D329
## 257 D33
## 258 D330
## 259 D331
## 260 D332
## 261 D333
## 262 D334
## 263 D335
## 264 D336
## 265 D337
## 266 D338
## 267 D339
## 268 D34
## 269 D340
## 270 D341
## 271 D342
## 272 D343
## 273 D344
## 274 D345
## 275 D346
## 276 D347
## 277 D348
## 278 D349
## 279 D35
## 280 D350
## 281 D351
## 282 D352
## 283 D353
## 284 D354
## 285 D355
## 286 D356
## 287 D357
## 288 D358
## 289 D359
## 290 D36
## 291 D360
## 292 D361
## 293 D362
## 294 D363
## 295 D364
## 296 D365
## 297 D366
## 298 D367
## 299 D368
## 300 D369
## 301 D37
## 302 D370
## 303 D371
## 304 D372
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## 309 D377
## 310 D378
## 311 D379
## 312 D38
## 313 D380
## 314 D381
## 315 D382
## 316 D383
## 317 D384
## 318 D385
## 319 D386
## 320 D387
## 321 D388
## 322 D389
## 323 D39
## 324 D390
## 325 D391
## 326 D392
## 327 D393
## 328 D394
## 329 D395
## 330 D396
## 331 D397
## 332 D398
## 333 D399
## 334 D4
## 335 D40
## 336 D400
## 337 D401
## 338 D402
## 339 D403
## 340 D404
## 341 D405
## 342 D406
## 343 D407
## 344 D408
## 345 D409
## 346 D41
## 347 D410
## 348 D411
## 349 D412
## 350 D413
## 351 D414
## 352 D415
## 353 D416
## 354 D417
## 355 D418
## 356 D419
## 357 D42
## 358 D420
## 359 D421
## 360 D422
## 361 D423
## 362 D424
## 363 D425
## 364 D426
## 365 D427
## 366 D428
## 367 D429
## 368 D43
## 369 D430
## 370 D431
## 371 D432
## 372 D433
## 373 D434
## 374 D435
## 375 D436
## 376 D437
## 377 D438
## 378 D439
## 379 D44
## 380 D440
## 381 D441
## 382 D442
## 383 D443
## 384 D444
## 385 D445
## 386 D446
## 387 D447
## 388 D448
## 389 D449
## 390 D45
## 391 D450
## 392 D451
## 393 D452
## 394 D453
## 395 D454
## 396 D455
## 397 D456
## 398 D457
## 399 D458
## 400 D459
## 401 D46
## 402 D460
## 403 D461
## 404 D462
## 405 D463
## 406 D464
## 407 D465
## 408 D466
## 409 D467
## 410 D468
## 411 D469
## 412 D47
## 413 D470
## 414 D471
## 415 D472
## 416 D473
## 417 D474
## 418 D475
## 419 D476
## 420 D477
## 421 D478
## 422 D479
## 423 D48
## 424 D480
## 425 D481
## 426 D482
## 427 D483
## 428 D484
## 429 D485
## 430 D486
## 431 D487
## 432 D488
## 433 D489
## 434 D49
## 435 D490
## 436 D491
## 437 D492
## 438 D493
## 439 D494
## 440 D495
## 441 D496
## 442 D497
## 443 D498
## 444 D499
## 445 D5
## 446 D50
## 447 D500
## 448 D51
## 449 D52
## 450 D53
## 451 D54
## 452 D55
## 453 D56
## 454 D57
## 455 D58
## 456 D59
## 457 D6
## 458 D60
## 459 D61
## 460 D62
## 461 D63
## 462 D64
## 463 D65
## 464 D66
## 465 D67
## 466 D68
## 467 D69
## 468 D7
## 469 D70
## 470 D71
## 471 D72
## 472 D73
## 473 D74
## 474 D75
## 475 D76
## 476 D77
## 477 D78
## 478 D79
## 479 D8
## 480 D80
## 481 D81
## 482 D82
## 483 D83
## 484 D84
## 485 D85
## 486 D86
## 487 D87
## 488 D88
## 489 D89
## 490 D9
## 491 D90
## 492 D91
## 493 D92
## 494 D93
## 495 D94
## 496 D95
## 497 D96
## 498 D97
## 499 D98
## 500 D99
## 501 D999The verb SELECT is one we’ll be using over and over again. Any time you want
to select data you also have to specify which table you want it from, so the
SELECT clause is always followed by a FROM clause. In this case, we asked
to see the column dragon_id from the dragons table. Sounds like English,
right?
If we want to see multiple columns, we can list them separated by commas:
## dragon_id sex
## 1 D1 F
## 2 D2 <NA>
## 3 D3 F
## 4 D4 F
## 5 D5 <NA>
## 6 D6 F
## 7 D7 M
## 8 D8 <NA>
## 9 D9 F
## 10 D10 F
## 11 D11 F
## 12 D12 F
## 13 D13 <NA>
## 14 D14 <NA>
## 15 D15 <NA>
## 16 D16 F
## 17 D17 F
## 18 D18 F
## 19 D19 F
## 20 D20 M
## 21 D21 F
## 22 D22 <NA>
## 23 D23 M
## 24 D24 <NA>
## 25 D25 M
## 26 D26 <NA>
## 27 D27 F
## 28 D28 M
## 29 D29 F
## 30 D30 F
## 31 D31 <NA>
## 32 D32 M
## 33 D33 F
## 34 D34 F
## 35 D35 F
## 36 D36 <NA>
## 37 D37 F
## 38 D38 F
## 39 D39 <NA>
## 40 D40 <NA>
## 41 D41 <NA>
## 42 D42 M
## 43 D43 F
## 44 D44 M
## 45 D45 F
## 46 D46 M
## 47 D47 F
## 48 D48 M
## 49 D49 <NA>
## 50 D50 F
## 51 D51 F
## 52 D52 M
## 53 D53 <NA>
## 54 D54 F
## 55 D55 <NA>
## 56 D56 F
## 57 D57 F
## 58 D58 M
## 59 D59 F
## 60 D60 F
## 61 D61 M
## 62 D62 F
## 63 D63 F
## 64 D64 <NA>
## 65 D65 <NA>
## 66 D66 <NA>
## 67 D67 M
## 68 D68 M
## 69 D69 F
## 70 D70 F
## 71 D71 M
## 72 D72 <NA>
## 73 D73 F
## 74 D74 <NA>
## 75 D75 M
## 76 D76 M
## 77 D77 <NA>
## 78 D78 <NA>
## 79 D79 M
## 80 D80 F
## 81 D81 <NA>
## 82 D82 F
## 83 D83 <NA>
## 84 D84 M
## 85 D85 F
## 86 D86 F
## 87 D87 M
## 88 D88 M
## 89 D89 F
## 90 D90 M
## 91 D91 F
## 92 D92 M
## 93 D93 M
## 94 D94 M
## 95 D95 M
## 96 D96 F
## 97 D97 <NA>
## 98 D98 <NA>
## 99 D99 F
## 100 D100 <NA>
## 101 D101 <NA>
## 102 D102 F
## 103 D103 F
## 104 D104 F
## 105 D105 M
## 106 D106 <NA>
## 107 D107 <NA>
## 108 D108 F
## 109 D109 M
## 110 D110 F
## 111 D111 M
## 112 D112 F
## 113 D113 <NA>
## 114 D114 <NA>
## 115 D115 F
## 116 D116 F
## 117 D117 <NA>
## 118 D118 <NA>
## 119 D119 F
## 120 D120 F
## 121 D121 <NA>
## 122 D122 F
## 123 D123 <NA>
## 124 D124 M
## 125 D125 <NA>
## 126 D126 M
## 127 D127 M
## 128 D128 <NA>
## 129 D129 M
## 130 D130 <NA>
## 131 D131 <NA>
## 132 D132 F
## 133 D133 F
## 134 D134 F
## 135 D135 <NA>
## 136 D136 F
## 137 D137 F
## 138 D138 F
## 139 D139 F
## 140 D140 <NA>
## 141 D141 F
## 142 D142 M
## 143 D143 F
## 144 D144 M
## 145 D145 M
## 146 D146 M
## 147 D147 <NA>
## 148 D148 <NA>
## 149 D149 M
## 150 D150 F
## 151 D151 <NA>
## 152 D152 F
## 153 D153 M
## 154 D154 F
## 155 D155 F
## 156 D156 M
## 157 D157 F
## 158 D158 <NA>
## 159 D159 <NA>
## 160 D160 F
## 161 D161 F
## 162 D162 F
## 163 D163 <NA>
## 164 D164 <NA>
## 165 D165 M
## 166 D166 <NA>
## 167 D167 M
## 168 D168 F
## 169 D169 F
## 170 D170 <NA>
## 171 D171 M
## 172 D172 M
## 173 D173 F
## 174 D174 <NA>
## 175 D175 M
## 176 D176 F
## 177 D177 F
## 178 D178 F
## 179 D179 <NA>
## 180 D180 F
## 181 D181 F
## 182 D182 F
## 183 D183 F
## 184 D184 F
## 185 D185 M
## 186 D186 <NA>
## 187 D187 <NA>
## 188 D188 M
## 189 D189 F
## 190 D190 F
## 191 D191 M
## 192 D192 M
## 193 D193 M
## 194 D194 <NA>
## 195 D195 F
## 196 D196 F
## 197 D197 F
## 198 D198 M
## 199 D199 <NA>
## 200 D200 <NA>
## 201 D201 <NA>
## 202 D202 M
## 203 D203 <NA>
## 204 D204 M
## 205 D205 F
## 206 D206 F
## 207 D207 <NA>
## 208 D208 M
## 209 D209 <NA>
## 210 D210 M
## 211 D211 F
## 212 D212 F
## 213 D213 <NA>
## 214 D214 F
## 215 D215 F
## 216 D216 <NA>
## 217 D217 F
## 218 D218 F
## 219 D219 M
## 220 D220 F
## 221 D221 M
## 222 D222 M
## 223 D223 M
## 224 D224 <NA>
## 225 D225 M
## 226 D226 <NA>
## 227 D227 F
## 228 D228 F
## 229 D229 <NA>
## 230 D230 M
## 231 D231 M
## 232 D232 F
## 233 D233 F
## 234 D234 F
## 235 D235 <NA>
## 236 D236 F
## 237 D237 M
## 238 D238 F
## 239 D239 F
## 240 D240 F
## 241 D241 <NA>
## 242 D242 M
## 243 D243 <NA>
## 244 D244 F
## 245 D245 <NA>
## 246 D246 <NA>
## 247 D247 M
## 248 D248 M
## 249 D249 <NA>
## 250 D250 F
## 251 D251 <NA>
## 252 D252 <NA>
## 253 D253 F
## 254 D254 F
## 255 D255 <NA>
## 256 D256 <NA>
## 257 D257 <NA>
## 258 D258 <NA>
## 259 D259 F
## 260 D260 F
## 261 D261 <NA>
## 262 D262 M
## 263 D263 M
## 264 D264 F
## 265 D265 M
## 266 D266 <NA>
## 267 D267 <NA>
## 268 D268 F
## 269 D269 F
## 270 D270 <NA>
## 271 D271 F
## 272 D272 F
## 273 D273 <NA>
## 274 D274 F
## 275 D275 F
## 276 D276 M
## 277 D277 F
## 278 D278 F
## 279 D279 <NA>
## 280 D280 M
## 281 D281 F
## 282 D282 F
## 283 D283 F
## 284 D284 F
## 285 D285 <NA>
## 286 D286 F
## 287 D287 M
## 288 D288 M
## 289 D289 <NA>
## 290 D290 <NA>
## 291 D291 F
## 292 D292 <NA>
## 293 D293 F
## 294 D294 F
## 295 D295 M
## 296 D296 <NA>
## 297 D297 <NA>
## 298 D298 M
## 299 D299 F
## 300 D300 F
## 301 D301 F
## 302 D302 F
## 303 D303 <NA>
## 304 D304 F
## 305 D305 M
## 306 D306 <NA>
## 307 D307 <NA>
## 308 D308 F
## 309 D309 <NA>
## 310 D310 <NA>
## 311 D311 M
## 312 D312 M
## 313 D313 F
## 314 D314 M
## 315 D315 F
## 316 D316 M
## 317 D317 F
## 318 D318 <NA>
## 319 D319 <NA>
## 320 D320 <NA>
## 321 D321 M
## 322 D322 <NA>
## 323 D323 M
## 324 D324 <NA>
## 325 D325 F
## 326 D326 F
## 327 D327 M
## 328 D328 <NA>
## 329 D329 M
## 330 D330 F
## 331 D331 <NA>
## 332 D332 F
## 333 D333 <NA>
## 334 D334 <NA>
## 335 D335 F
## 336 D336 <NA>
## 337 D337 M
## 338 D338 <NA>
## 339 D339 <NA>
## 340 D340 <NA>
## 341 D341 F
## 342 D342 <NA>
## 343 D343 F
## 344 D344 <NA>
## 345 D345 M
## 346 D346 F
## 347 D347 F
## 348 D348 <NA>
## 349 D349 M
## 350 D350 M
## 351 D351 M
## 352 D352 M
## 353 D353 <NA>
## 354 D354 F
## 355 D355 <NA>
## 356 D356 F
## 357 D357 F
## 358 D358 <NA>
## 359 D359 F
## 360 D360 M
## 361 D361 M
## 362 D362 F
## 363 D363 <NA>
## 364 D364 <NA>
## 365 D365 M
## 366 D366 M
## 367 D367 M
## 368 D368 F
## 369 D369 M
## 370 D370 <NA>
## 371 D371 <NA>
## 372 D372 M
## 373 D373 F
## 374 D374 M
## 375 D375 M
## 376 D376 <NA>
## 377 D377 F
## 378 D378 M
## 379 D379 F
## 380 D380 <NA>
## 381 D381 M
## 382 D382 F
## 383 D383 F
## 384 D384 M
## 385 D385 F
## 386 D386 <NA>
## 387 D387 M
## 388 D388 F
## 389 D389 F
## 390 D390 F
## 391 D391 <NA>
## 392 D392 M
## 393 D393 M
## 394 D394 M
## 395 D395 <NA>
## 396 D396 F
## 397 D397 <NA>
## 398 D398 F
## 399 D399 F
## 400 D400 <NA>
## 401 D401 M
## 402 D402 F
## 403 D403 <NA>
## 404 D404 F
## 405 D405 M
## 406 D406 M
## 407 D407 M
## 408 D408 F
## 409 D409 <NA>
## 410 D410 F
## 411 D411 <NA>
## 412 D412 <NA>
## 413 D413 F
## 414 D414 F
## 415 D415 F
## 416 D416 F
## 417 D417 M
## 418 D418 M
## 419 D419 F
## 420 D420 <NA>
## 421 D421 <NA>
## 422 D422 F
## 423 D423 M
## 424 D424 F
## 425 D425 M
## 426 D426 F
## 427 D427 F
## 428 D428 <NA>
## 429 D429 <NA>
## 430 D430 F
## 431 D431 <NA>
## 432 D432 M
## 433 D433 M
## 434 D434 <NA>
## 435 D435 <NA>
## 436 D436 <NA>
## 437 D437 M
## 438 D438 <NA>
## 439 D439 F
## 440 D440 M
## 441 D441 F
## 442 D442 M
## 443 D443 F
## 444 D444 M
## 445 D445 M
## 446 D446 F
## 447 D447 <NA>
## 448 D448 F
## 449 D449 M
## 450 D450 F
## 451 D451 F
## 452 D452 F
## 453 D453 F
## 454 D454 M
## 455 D455 F
## 456 D456 F
## 457 D457 F
## 458 D458 F
## 459 D459 F
## 460 D460 F
## 461 D461 M
## 462 D462 <NA>
## 463 D463 M
## 464 D464 F
## 465 D465 M
## 466 D466 <NA>
## 467 D467 <NA>
## 468 D468 M
## 469 D469 F
## 470 D470 F
## 471 D471 F
## 472 D472 M
## 473 D473 M
## 474 D474 F
## 475 D475 M
## 476 D476 F
## 477 D477 M
## 478 D478 M
## 479 D479 F
## 480 D480 F
## 481 D481 F
## 482 D482 M
## 483 D483 <NA>
## 484 D484 M
## 485 D485 M
## 486 D486 <NA>
## 487 D487 F
## 488 D488 <NA>
## 489 D489 F
## 490 D490 F
## 491 D491 F
## 492 D492 F
## 493 D493 F
## 494 D494 F
## 495 D495 M
## 496 D496 F
## 497 D497 F
## 498 D498 F
## 499 D499 F
## 500 D500 F
## 501 D999 FAnd if we want to see the whole table (not specific columns), we can use a wildcard:
## dragon_id sex age_class species update_timestamp
## 1 D1 F Subadult Hebridean Black <NA>
## 2 D2 <NA> Juvenile Romanian Longhorn <NA>
## 3 D3 F Adult Hebridean Black <NA>
## 4 D4 F Adult Peruvian Vipertooth <NA>
## 5 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 6 D6 F Adult Norwegian Ridgeback <NA>
## 7 D7 M Adult Hebridean Black <NA>
## 8 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 9 D9 F Adult Norwegian Ridgeback <NA>
## 10 D10 F Adult Common Welsh Green <NA>
## 11 D11 F Adult Peruvian Vipertooth <NA>
## 12 D12 F Adult Swedish Short-Snout <NA>
## 13 D13 <NA> Juvenile Peruvian Vipertooth <NA>
## 14 D14 <NA> Juvenile Hebridean Black <NA>
## 15 D15 <NA> Juvenile Chinese Fireball <NA>
## 16 D16 F Adult Chinese Fireball <NA>
## 17 D17 F Adult Peruvian Vipertooth <NA>
## 18 D18 F Adult Norwegian Ridgeback <NA>
## 19 D19 F Adult Common Welsh Green <NA>
## 20 D20 M Subadult Chinese Fireball <NA>
## 21 D21 F Adult Ukrainian Ironbelly <NA>
## 22 D22 <NA> Juvenile Norwegian Ridgeback <NA>
## 23 D23 M Adult Swedish Short-Snout <NA>
## 24 D24 <NA> Juvenile Common Welsh Green <NA>
## 25 D25 M Adult Peruvian Vipertooth <NA>
## 26 D26 <NA> Juvenile Common Welsh Green <NA>
## 27 D27 F Adult Norwegian Ridgeback <NA>
## 28 D28 M Adult Common Welsh Green <NA>
## 29 D29 F Adult Norwegian Ridgeback <NA>
## 30 D30 F Adult Chinese Fireball <NA>
## 31 D31 <NA> Juvenile Common Welsh Green <NA>
## 32 D32 M Adult Ukrainian Ironbelly <NA>
## 33 D33 F Adult Romanian Longhorn <NA>
## 34 D34 F Adult Norwegian Ridgeback <NA>
## 35 D35 F Adult Ukrainian Ironbelly <NA>
## 36 D36 <NA> Juvenile Romanian Longhorn <NA>
## 37 D37 F Subadult Common Welsh Green <NA>
## 38 D38 F Adult Hungarian Horntail <NA>
## 39 D39 <NA> Juvenile Antipodean Opaleye <NA>
## 40 D40 <NA> Juvenile Common Welsh Green <NA>
## 41 D41 <NA> Juvenile Ukrainian Ironbelly <NA>
## 42 D42 M Adult Swedish Short-Snout <NA>
## 43 D43 F Subadult Antipodean Opaleye <NA>
## 44 D44 M Adult Romanian Longhorn <NA>
## 45 D45 F Adult Peruvian Vipertooth <NA>
## 46 D46 M Subadult Hebridean Black <NA>
## 47 D47 F Adult Ukrainian Ironbelly <NA>
## 48 D48 M Adult Ukrainian Ironbelly <NA>
## 49 D49 <NA> Juvenile Common Welsh Green <NA>
## 50 D50 F Adult Chinese Fireball <NA>
## 51 D51 F Subadult Norwegian Ridgeback <NA>
## 52 D52 M Adult Common Welsh Green <NA>
## 53 D53 <NA> Juvenile Norwegian Ridgeback <NA>
## 54 D54 F Adult Norwegian Ridgeback <NA>
## 55 D55 <NA> Juvenile Common Welsh Green <NA>
## 56 D56 F Subadult Norwegian Ridgeback <NA>
## 57 D57 F Adult Common Welsh Green <NA>
## 58 D58 M Adult Hebridean Black <NA>
## 59 D59 F Adult Peruvian Vipertooth <NA>
## 60 D60 F Adult Hebridean Black <NA>
## 61 D61 M Subadult Romanian Longhorn <NA>
## 62 D62 F Adult Hungarian Horntail <NA>
## 63 D63 F Adult Antipodean Opaleye <NA>
## 64 D64 <NA> Juvenile Romanian Longhorn <NA>
## 65 D65 <NA> Juvenile Romanian Longhorn <NA>
## 66 D66 <NA> Juvenile Ukrainian Ironbelly <NA>
## 67 D67 M Adult Norwegian Ridgeback <NA>
## 68 D68 M Adult Antipodean Opaleye <NA>
## 69 D69 F Subadult Hebridean Black <NA>
## 70 D70 F Adult Norwegian Ridgeback <NA>
## 71 D71 M Adult Hebridean Black <NA>
## 72 D72 <NA> Juvenile Common Welsh Green <NA>
## 73 D73 F Adult Romanian Longhorn <NA>
## 74 D74 <NA> Juvenile Antipodean Opaleye <NA>
## 75 D75 M Adult Swedish Short-Snout <NA>
## 76 D76 M Adult Romanian Longhorn <NA>
## 77 D77 <NA> Juvenile Hebridean Black <NA>
## 78 D78 <NA> Juvenile Norwegian Ridgeback <NA>
## 79 D79 M Adult Common Welsh Green <NA>
## 80 D80 F Adult Romanian Longhorn <NA>
## 81 D81 <NA> Juvenile Norwegian Ridgeback <NA>
## 82 D82 F Adult Hebridean Black <NA>
## 83 D83 <NA> Juvenile Peruvian Vipertooth <NA>
## 84 D84 M Adult Norwegian Ridgeback <NA>
## 85 D85 F Adult Hebridean Black <NA>
## 86 D86 F Adult Hebridean Black <NA>
## 87 D87 M Adult Hungarian Horntail <NA>
## 88 D88 M Adult Swedish Short-Snout <NA>
## 89 D89 F Adult Norwegian Ridgeback <NA>
## 90 D90 M Adult Peruvian Vipertooth <NA>
## 91 D91 F Adult Hebridean Black <NA>
## 92 D92 M Adult Hebridean Black <NA>
## 93 D93 M Subadult Peruvian Vipertooth <NA>
## 94 D94 M Adult Romanian Longhorn <NA>
## 95 D95 M Adult Romanian Longhorn <NA>
## 96 D96 F Adult Common Welsh Green <NA>
## 97 D97 <NA> Juvenile Chinese Fireball <NA>
## 98 D98 <NA> Juvenile Hebridean Black <NA>
## 99 D99 F Adult Hebridean Black <NA>
## 100 D100 <NA> Juvenile Common Welsh Green <NA>
## 101 D101 <NA> Juvenile Hungarian Horntail <NA>
## 102 D102 F Subadult Hungarian Horntail <NA>
## 103 D103 F Adult Hebridean Black <NA>
## 104 D104 F Adult Hebridean Black <NA>
## 105 D105 M Adult Common Welsh Green <NA>
## 106 D106 <NA> Juvenile Peruvian Vipertooth <NA>
## 107 D107 <NA> Juvenile Hungarian Horntail <NA>
## 108 D108 F Adult Norwegian Ridgeback <NA>
## 109 D109 M Adult Swedish Short-Snout <NA>
## 110 D110 F Adult Peruvian Vipertooth <NA>
## 111 D111 M Adult Norwegian Ridgeback <NA>
## 112 D112 F Adult Peruvian Vipertooth <NA>
## 113 D113 <NA> Juvenile Romanian Longhorn <NA>
## 114 D114 <NA> Juvenile Chinese Fireball <NA>
## 115 D115 F Adult Common Welsh Green <NA>
## 116 D116 F Adult Norwegian Ridgeback <NA>
## 117 D117 <NA> Juvenile Antipodean Opaleye <NA>
## 118 D118 <NA> Juvenile Hungarian Horntail <NA>
## 119 D119 F Adult Norwegian Ridgeback <NA>
## 120 D120 F Adult Hebridean Black <NA>
## 121 D121 <NA> Juvenile Common Welsh Green <NA>
## 122 D122 F Adult Ukrainian Ironbelly <NA>
## 123 D123 <NA> Juvenile Common Welsh Green <NA>
## 124 D124 M Adult Chinese Fireball <NA>
## 125 D125 <NA> Juvenile Swedish Short-Snout <NA>
## 126 D126 M Adult Swedish Short-Snout <NA>
## 127 D127 M Subadult Ukrainian Ironbelly <NA>
## 128 D128 <NA> Juvenile Norwegian Ridgeback <NA>
## 129 D129 M Adult Romanian Longhorn <NA>
## 130 D130 <NA> Juvenile Peruvian Vipertooth <NA>
## 131 D131 <NA> Juvenile Norwegian Ridgeback <NA>
## 132 D132 F Adult Norwegian Ridgeback <NA>
## 133 D133 F Adult Ukrainian Ironbelly <NA>
## 134 D134 F Adult Hebridean Black <NA>
## 135 D135 <NA> Juvenile Peruvian Vipertooth <NA>
## 136 D136 F Subadult Chinese Fireball <NA>
## 137 D137 F Adult Antipodean Opaleye <NA>
## 138 D138 F Adult Common Welsh Green <NA>
## 139 D139 F Adult Hebridean Black <NA>
## 140 D140 <NA> Juvenile Hebridean Black <NA>
## 141 D141 F Adult Romanian Longhorn <NA>
## 142 D142 M Subadult Common Welsh Green <NA>
## 143 D143 F Adult Antipodean Opaleye <NA>
## 144 D144 M Adult Norwegian Ridgeback <NA>
## 145 D145 M Adult Norwegian Ridgeback <NA>
## 146 D146 M Adult Norwegian Ridgeback <NA>
## 147 D147 <NA> Juvenile Common Welsh Green <NA>
## 148 D148 <NA> Juvenile Romanian Longhorn <NA>
## 149 D149 M Adult Norwegian Ridgeback <NA>
## 150 D150 F Adult Hungarian Horntail <NA>
## 151 D151 <NA> Juvenile Common Welsh Green <NA>
## 152 D152 F Subadult Peruvian Vipertooth <NA>
## 153 D153 M Adult Antipodean Opaleye <NA>
## 154 D154 F Adult Hebridean Black <NA>
## 155 D155 F Adult Common Welsh Green <NA>
## 156 D156 M Adult Peruvian Vipertooth <NA>
## 157 D157 F Subadult Swedish Short-Snout <NA>
## 158 D158 <NA> Juvenile Ukrainian Ironbelly <NA>
## 159 D159 <NA> Juvenile Common Welsh Green <NA>
## 160 D160 F Adult Common Welsh Green <NA>
## 161 D161 F Adult Chinese Fireball <NA>
## 162 D162 F Adult Hungarian Horntail <NA>
## 163 D163 <NA> Juvenile Peruvian Vipertooth <NA>
## 164 D164 <NA> Juvenile Chinese Fireball <NA>
## 165 D165 M Adult Hungarian Horntail <NA>
## 166 D166 <NA> Juvenile Swedish Short-Snout <NA>
## 167 D167 M Adult Norwegian Ridgeback <NA>
## 168 D168 F Adult Swedish Short-Snout <NA>
## 169 D169 F Adult Hebridean Black <NA>
## 170 D170 <NA> Juvenile Norwegian Ridgeback <NA>
## 171 D171 M Subadult Ukrainian Ironbelly <NA>
## 172 D172 M Adult Peruvian Vipertooth <NA>
## 173 D173 F Adult Swedish Short-Snout <NA>
## 174 D174 <NA> Juvenile Romanian Longhorn <NA>
## 175 D175 M Adult Chinese Fireball <NA>
## 176 D176 F Adult Ukrainian Ironbelly <NA>
## 177 D177 F Adult Romanian Longhorn <NA>
## 178 D178 F Adult Hebridean Black <NA>
## 179 D179 <NA> Juvenile Common Welsh Green <NA>
## 180 D180 F Adult Norwegian Ridgeback <NA>
## 181 D181 F Adult Common Welsh Green <NA>
## 182 D182 F Adult Common Welsh Green <NA>
## 183 D183 F Adult Common Welsh Green <NA>
## 184 D184 F Adult Norwegian Ridgeback <NA>
## 185 D185 M Adult Chinese Fireball <NA>
## 186 D186 <NA> Juvenile Common Welsh Green <NA>
## 187 D187 <NA> Juvenile Hebridean Black <NA>
## 188 D188 M Adult Hungarian Horntail <NA>
## 189 D189 F Adult Hungarian Horntail <NA>
## 190 D190 F Adult Hebridean Black <NA>
## 191 D191 M Adult Peruvian Vipertooth <NA>
## 192 D192 M Adult Norwegian Ridgeback <NA>
## 193 D193 M Adult Peruvian Vipertooth <NA>
## 194 D194 <NA> Juvenile Romanian Longhorn <NA>
## 195 D195 F Adult Romanian Longhorn <NA>
## 196 D196 F Adult Romanian Longhorn <NA>
## 197 D197 F Adult Hungarian Horntail <NA>
## 198 D198 M Adult Ukrainian Ironbelly <NA>
## 199 D199 <NA> Juvenile Hungarian Horntail <NA>
## 200 D200 <NA> Juvenile Hungarian Horntail <NA>
## 201 D201 <NA> Juvenile Common Welsh Green <NA>
## 202 D202 M Adult Common Welsh Green <NA>
## 203 D203 <NA> Juvenile Romanian Longhorn <NA>
## 204 D204 M Adult Romanian Longhorn <NA>
## 205 D205 F Adult Hungarian Horntail <NA>
## 206 D206 F Adult Hungarian Horntail <NA>
## 207 D207 <NA> Juvenile Romanian Longhorn <NA>
## 208 D208 M Adult Norwegian Ridgeback <NA>
## 209 D209 <NA> Juvenile Norwegian Ridgeback <NA>
## 210 D210 M Adult Norwegian Ridgeback <NA>
## 211 D211 F Adult Hebridean Black <NA>
## 212 D212 F Adult Antipodean Opaleye <NA>
## 213 D213 <NA> Juvenile Hebridean Black <NA>
## 214 D214 F Subadult Hungarian Horntail <NA>
## 215 D215 F Adult Norwegian Ridgeback <NA>
## 216 D216 <NA> Juvenile Antipodean Opaleye <NA>
## 217 D217 F Adult Peruvian Vipertooth <NA>
## 218 D218 F Adult Hebridean Black <NA>
## 219 D219 M Adult Peruvian Vipertooth <NA>
## 220 D220 F Adult Common Welsh Green <NA>
## 221 D221 M Adult Peruvian Vipertooth <NA>
## 222 D222 M Subadult Hungarian Horntail <NA>
## 223 D223 M Adult Antipodean Opaleye <NA>
## 224 D224 <NA> Juvenile Peruvian Vipertooth <NA>
## 225 D225 M Adult Norwegian Ridgeback <NA>
## 226 D226 <NA> Juvenile Swedish Short-Snout <NA>
## 227 D227 F Adult Romanian Longhorn <NA>
## 228 D228 F Adult Hebridean Black <NA>
## 229 D229 <NA> Juvenile Hungarian Horntail <NA>
## 230 D230 M Adult Norwegian Ridgeback <NA>
## 231 D231 M Adult Norwegian Ridgeback <NA>
## 232 D232 F Subadult Hebridean Black <NA>
## 233 D233 F Subadult Romanian Longhorn <NA>
## 234 D234 F Adult Norwegian Ridgeback <NA>
## 235 D235 <NA> Juvenile Hebridean Black <NA>
## 236 D236 F Adult Hungarian Horntail <NA>
## 237 D237 M Adult Hungarian Horntail <NA>
## 238 D238 F Adult Swedish Short-Snout <NA>
## 239 D239 F Adult Hebridean Black <NA>
## 240 D240 F Adult Ukrainian Ironbelly <NA>
## 241 D241 <NA> Juvenile Norwegian Ridgeback <NA>
## 242 D242 M Adult Romanian Longhorn <NA>
## 243 D243 <NA> Juvenile Peruvian Vipertooth <NA>
## 244 D244 F Adult Hungarian Horntail <NA>
## 245 D245 <NA> Juvenile Norwegian Ridgeback <NA>
## 246 D246 <NA> Juvenile Peruvian Vipertooth <NA>
## 247 D247 M Adult Norwegian Ridgeback <NA>
## 248 D248 M Subadult Common Welsh Green <NA>
## 249 D249 <NA> Juvenile Romanian Longhorn <NA>
## 250 D250 F Adult Romanian Longhorn <NA>
## 251 D251 <NA> Juvenile Peruvian Vipertooth <NA>
## 252 D252 <NA> Juvenile Common Welsh Green <NA>
## 253 D253 F Adult Norwegian Ridgeback <NA>
## 254 D254 F Adult Romanian Longhorn <NA>
## 255 D255 <NA> Juvenile Hungarian Horntail <NA>
## 256 D256 <NA> Juvenile Norwegian Ridgeback <NA>
## 257 D257 <NA> Juvenile Norwegian Ridgeback <NA>
## 258 D258 <NA> Juvenile Peruvian Vipertooth <NA>
## 259 D259 F Adult Hebridean Black <NA>
## 260 D260 F Adult Common Welsh Green <NA>
## 261 D261 <NA> Juvenile Norwegian Ridgeback <NA>
## 262 D262 M Adult Peruvian Vipertooth <NA>
## 263 D263 M Adult Hebridean Black <NA>
## 264 D264 F Subadult Norwegian Ridgeback <NA>
## 265 D265 M Adult Hebridean Black <NA>
## 266 D266 <NA> Juvenile Swedish Short-Snout <NA>
## 267 D267 <NA> Juvenile Norwegian Ridgeback <NA>
## 268 D268 F Adult Romanian Longhorn <NA>
## 269 D269 F Adult Swedish Short-Snout <NA>
## 270 D270 <NA> Juvenile Norwegian Ridgeback <NA>
## 271 D271 F Adult Romanian Longhorn <NA>
## 272 D272 F Adult Romanian Longhorn <NA>
## 273 D273 <NA> Juvenile Common Welsh Green <NA>
## 274 D274 F Adult Norwegian Ridgeback <NA>
## 275 D275 F Adult Hebridean Black <NA>
## 276 D276 M Adult Norwegian Ridgeback <NA>
## 277 D277 F Subadult Swedish Short-Snout <NA>
## 278 D278 F Adult Common Welsh Green <NA>
## 279 D279 <NA> Juvenile Norwegian Ridgeback <NA>
## 280 D280 M Adult Ukrainian Ironbelly <NA>
## 281 D281 F Adult Romanian Longhorn <NA>
## 282 D282 F Adult Peruvian Vipertooth <NA>
## 283 D283 F Adult Common Welsh Green <NA>
## 284 D284 F Adult Romanian Longhorn <NA>
## 285 D285 <NA> Juvenile Hebridean Black <NA>
## 286 D286 F Adult Ukrainian Ironbelly <NA>
## 287 D287 M Adult Norwegian Ridgeback <NA>
## 288 D288 M Subadult Hebridean Black <NA>
## 289 D289 <NA> Juvenile Ukrainian Ironbelly <NA>
## 290 D290 <NA> Juvenile Common Welsh Green <NA>
## 291 D291 F Adult Hebridean Black <NA>
## 292 D292 <NA> Juvenile Hebridean Black <NA>
## 293 D293 F Adult Chinese Fireball <NA>
## 294 D294 F Adult Common Welsh Green <NA>
## 295 D295 M Subadult Antipodean Opaleye <NA>
## 296 D296 <NA> Juvenile Hungarian Horntail <NA>
## 297 D297 <NA> Juvenile Hebridean Black <NA>
## 298 D298 M Adult Peruvian Vipertooth <NA>
## 299 D299 F Adult Romanian Longhorn <NA>
## 300 D300 F Adult Peruvian Vipertooth <NA>
## 301 D301 F Subadult Common Welsh Green <NA>
## 302 D302 F Adult Ukrainian Ironbelly <NA>
## 303 D303 <NA> Juvenile Antipodean Opaleye <NA>
## 304 D304 F Subadult Romanian Longhorn <NA>
## 305 D305 M Adult Common Welsh Green <NA>
## 306 D306 <NA> Juvenile Common Welsh Green <NA>
## 307 D307 <NA> Juvenile Ukrainian Ironbelly <NA>
## 308 D308 F Adult Romanian Longhorn <NA>
## 309 D309 <NA> Juvenile Peruvian Vipertooth <NA>
## 310 D310 <NA> Juvenile Common Welsh Green <NA>
## 311 D311 M Adult Norwegian Ridgeback <NA>
## 312 D312 M Subadult Chinese Fireball <NA>
## 313 D313 F Adult Antipodean Opaleye <NA>
## 314 D314 M Adult Romanian Longhorn <NA>
## 315 D315 F Adult Common Welsh Green <NA>
## 316 D316 M Subadult Hebridean Black <NA>
## 317 D317 F Adult Antipodean Opaleye <NA>
## 318 D318 <NA> Juvenile Peruvian Vipertooth <NA>
## 319 D319 <NA> Juvenile Swedish Short-Snout <NA>
## 320 D320 <NA> Juvenile Hungarian Horntail <NA>
## 321 D321 M Adult Norwegian Ridgeback <NA>
## 322 D322 <NA> Juvenile Chinese Fireball <NA>
## 323 D323 M Adult Romanian Longhorn <NA>
## 324 D324 <NA> Juvenile Common Welsh Green <NA>
## 325 D325 F Adult Norwegian Ridgeback <NA>
## 326 D326 F Adult Ukrainian Ironbelly <NA>
## 327 D327 M Subadult Romanian Longhorn <NA>
## 328 D328 <NA> Juvenile Norwegian Ridgeback <NA>
## 329 D329 M Adult Romanian Longhorn <NA>
## 330 D330 F Adult Peruvian Vipertooth <NA>
## 331 D331 <NA> Juvenile Swedish Short-Snout <NA>
## 332 D332 F Subadult Common Welsh Green <NA>
## 333 D333 <NA> Juvenile Norwegian Ridgeback <NA>
## 334 D334 <NA> Juvenile Romanian Longhorn <NA>
## 335 D335 F Adult Romanian Longhorn <NA>
## 336 D336 <NA> Juvenile Common Welsh Green <NA>
## 337 D337 M Adult Peruvian Vipertooth <NA>
## 338 D338 <NA> Juvenile Antipodean Opaleye <NA>
## 339 D339 <NA> Juvenile Chinese Fireball <NA>
## 340 D340 <NA> Juvenile Antipodean Opaleye <NA>
## 341 D341 F Adult Norwegian Ridgeback <NA>
## 342 D342 <NA> Juvenile Peruvian Vipertooth <NA>
## 343 D343 F Adult Antipodean Opaleye <NA>
## 344 D344 <NA> Juvenile Romanian Longhorn <NA>
## 345 D345 M Adult Swedish Short-Snout <NA>
## 346 D346 F Adult Romanian Longhorn <NA>
## 347 D347 F Subadult Common Welsh Green <NA>
## 348 D348 <NA> Juvenile Norwegian Ridgeback <NA>
## 349 D349 M Adult Peruvian Vipertooth <NA>
## 350 D350 M Adult Hebridean Black <NA>
## 351 D351 M Adult Peruvian Vipertooth <NA>
## 352 D352 M Adult Romanian Longhorn <NA>
## 353 D353 <NA> Juvenile Hebridean Black <NA>
## 354 D354 F Adult Norwegian Ridgeback <NA>
## 355 D355 <NA> Juvenile Hungarian Horntail <NA>
## 356 D356 F Adult Romanian Longhorn <NA>
## 357 D357 F Subadult Romanian Longhorn <NA>
## 358 D358 <NA> Juvenile Common Welsh Green <NA>
## 359 D359 F Adult Hebridean Black <NA>
## 360 D360 M Adult Norwegian Ridgeback <NA>
## 361 D361 M Adult Swedish Short-Snout <NA>
## 362 D362 F Subadult Norwegian Ridgeback <NA>
## 363 D363 <NA> Juvenile Romanian Longhorn <NA>
## 364 D364 <NA> Juvenile Common Welsh Green <NA>
## 365 D365 M Adult Romanian Longhorn <NA>
## 366 D366 M Adult Norwegian Ridgeback <NA>
## 367 D367 M Adult Peruvian Vipertooth <NA>
## 368 D368 F Adult Common Welsh Green <NA>
## 369 D369 M Adult Norwegian Ridgeback <NA>
## 370 D370 <NA> Juvenile Common Welsh Green <NA>
## 371 D371 <NA> Juvenile Ukrainian Ironbelly <NA>
## 372 D372 M Adult Peruvian Vipertooth <NA>
## 373 D373 F Adult Peruvian Vipertooth <NA>
## 374 D374 M Adult Swedish Short-Snout <NA>
## 375 D375 M Adult Norwegian Ridgeback <NA>
## 376 D376 <NA> Juvenile Swedish Short-Snout <NA>
## 377 D377 F Adult Hebridean Black <NA>
## 378 D378 M Adult Romanian Longhorn <NA>
## 379 D379 F Adult Antipodean Opaleye <NA>
## 380 D380 <NA> Juvenile Norwegian Ridgeback <NA>
## 381 D381 M Adult Common Welsh Green <NA>
## 382 D382 F Adult Norwegian Ridgeback <NA>
## 383 D383 F Adult Hebridean Black <NA>
## 384 D384 M Adult Hungarian Horntail <NA>
## 385 D385 F Adult Common Welsh Green <NA>
## 386 D386 <NA> Juvenile Norwegian Ridgeback <NA>
## 387 D387 M Adult Hebridean Black <NA>
## 388 D388 F Subadult Common Welsh Green <NA>
## 389 D389 F Adult Hebridean Black <NA>
## 390 D390 F Adult Common Welsh Green <NA>
## 391 D391 <NA> Juvenile Norwegian Ridgeback <NA>
## 392 D392 M Adult Peruvian Vipertooth <NA>
## 393 D393 M Adult Hebridean Black <NA>
## 394 D394 M Adult Swedish Short-Snout <NA>
## 395 D395 <NA> Juvenile Antipodean Opaleye <NA>
## 396 D396 F Subadult Norwegian Ridgeback <NA>
## 397 D397 <NA> Juvenile Ukrainian Ironbelly <NA>
## 398 D398 F Adult Common Welsh Green <NA>
## 399 D399 F Adult Romanian Longhorn <NA>
## 400 D400 <NA> Juvenile Hungarian Horntail <NA>
## 401 D401 M Subadult Norwegian Ridgeback <NA>
## 402 D402 F Adult Common Welsh Green <NA>
## 403 D403 <NA> Juvenile Common Welsh Green <NA>
## 404 D404 F Adult Common Welsh Green <NA>
## 405 D405 M Adult Romanian Longhorn <NA>
## 406 D406 M Adult Hebridean Black <NA>
## 407 D407 M Adult Antipodean Opaleye <NA>
## 408 D408 F Adult Common Welsh Green <NA>
## 409 D409 <NA> Juvenile Norwegian Ridgeback <NA>
## 410 D410 F Adult Hebridean Black <NA>
## 411 D411 <NA> Juvenile Peruvian Vipertooth <NA>
## 412 D412 <NA> Juvenile Romanian Longhorn <NA>
## 413 D413 F Adult Romanian Longhorn <NA>
## 414 D414 F Adult Peruvian Vipertooth <NA>
## 415 D415 F Adult Romanian Longhorn <NA>
## 416 D416 F Adult Romanian Longhorn <NA>
## 417 D417 M Adult Norwegian Ridgeback <NA>
## 418 D418 M Subadult Common Welsh Green <NA>
## 419 D419 F Adult Norwegian Ridgeback <NA>
## 420 D420 <NA> Juvenile Common Welsh Green <NA>
## 421 D421 <NA> Juvenile Common Welsh Green <NA>
## 422 D422 F Adult Norwegian Ridgeback <NA>
## 423 D423 M Adult Common Welsh Green <NA>
## 424 D424 F Adult Hebridean Black <NA>
## 425 D425 M Adult Romanian Longhorn <NA>
## 426 D426 F Adult Norwegian Ridgeback <NA>
## 427 D427 F Adult Peruvian Vipertooth <NA>
## 428 D428 <NA> Juvenile Common Welsh Green <NA>
## 429 D429 <NA> Juvenile Common Welsh Green <NA>
## 430 D430 F Adult Hungarian Horntail <NA>
## 431 D431 <NA> Juvenile Ukrainian Ironbelly <NA>
## 432 D432 M Adult Antipodean Opaleye <NA>
## 433 D433 M Adult Peruvian Vipertooth <NA>
## 434 D434 <NA> Juvenile Peruvian Vipertooth <NA>
## 435 D435 <NA> Juvenile Peruvian Vipertooth <NA>
## 436 D436 <NA> Juvenile Romanian Longhorn <NA>
## 437 D437 M Adult Common Welsh Green <NA>
## 438 D438 <NA> Juvenile Norwegian Ridgeback <NA>
## 439 D439 F Subadult Hungarian Horntail <NA>
## 440 D440 M Adult Common Welsh Green <NA>
## 441 D441 F Adult Norwegian Ridgeback <NA>
## 442 D442 M Adult Romanian Longhorn <NA>
## 443 D443 F Adult Hebridean Black <NA>
## 444 D444 M Adult Hebridean Black <NA>
## 445 D445 M Adult Norwegian Ridgeback <NA>
## 446 D446 F Adult Swedish Short-Snout <NA>
## 447 D447 <NA> Juvenile Romanian Longhorn <NA>
## 448 D448 F Adult Peruvian Vipertooth <NA>
## 449 D449 M Adult Chinese Fireball <NA>
## 450 D450 F Adult Peruvian Vipertooth <NA>
## 451 D451 F Adult Common Welsh Green <NA>
## 452 D452 F Adult Swedish Short-Snout <NA>
## 453 D453 F Adult Antipodean Opaleye <NA>
## 454 D454 M Adult Romanian Longhorn <NA>
## 455 D455 F Adult Common Welsh Green <NA>
## 456 D456 F Adult Peruvian Vipertooth <NA>
## 457 D457 F Adult Antipodean Opaleye <NA>
## 458 D458 F Adult Romanian Longhorn <NA>
## 459 D459 F Subadult Swedish Short-Snout <NA>
## 460 D460 F Adult Norwegian Ridgeback <NA>
## 461 D461 M Adult Hebridean Black <NA>
## 462 D462 <NA> Juvenile Common Welsh Green <NA>
## 463 D463 M Adult Peruvian Vipertooth <NA>
## 464 D464 F Adult Hebridean Black <NA>
## 465 D465 M Adult Hungarian Horntail <NA>
## 466 D466 <NA> Juvenile Peruvian Vipertooth <NA>
## 467 D467 <NA> Juvenile Hungarian Horntail <NA>
## 468 D468 M Adult Peruvian Vipertooth <NA>
## 469 D469 F Adult Romanian Longhorn <NA>
## 470 D470 F Adult Hungarian Horntail <NA>
## 471 D471 F Adult Peruvian Vipertooth <NA>
## 472 D472 M Adult Hungarian Horntail <NA>
## 473 D473 M Adult Peruvian Vipertooth <NA>
## 474 D474 F Adult Ukrainian Ironbelly <NA>
## 475 D475 M Subadult Norwegian Ridgeback <NA>
## 476 D476 F Adult Norwegian Ridgeback <NA>
## 477 D477 M Adult Norwegian Ridgeback <NA>
## 478 D478 M Adult Common Welsh Green <NA>
## 479 D479 F Adult Chinese Fireball <NA>
## 480 D480 F Adult Hebridean Black <NA>
## 481 D481 F Adult Hungarian Horntail <NA>
## 482 D482 M Subadult Romanian Longhorn <NA>
## 483 D483 <NA> Juvenile Hebridean Black <NA>
## 484 D484 M Adult Hebridean Black <NA>
## 485 D485 M Adult Hebridean Black <NA>
## 486 D486 <NA> Juvenile Common Welsh Green <NA>
## 487 D487 F Adult Hungarian Horntail <NA>
## 488 D488 <NA> Juvenile Hungarian Horntail <NA>
## 489 D489 F Adult Common Welsh Green <NA>
## 490 D490 F Adult Romanian Longhorn <NA>
## 491 D491 F Adult Hebridean Black <NA>
## 492 D492 F Adult Hungarian Horntail <NA>
## 493 D493 F Adult Hebridean Black <NA>
## 494 D494 F Adult Chinese Fireball <NA>
## 495 D495 M Adult Romanian Longhorn <NA>
## 496 D496 F Adult Romanian Longhorn <NA>
## 497 D497 F Adult Hungarian Horntail <NA>
## 498 D498 F Adult Common Welsh Green <NA>
## 499 D499 F Adult Peruvian Vipertooth <NA>
## 500 D500 F Adult Common Welsh Green <NA>
## 501 D999 F Adult Norwegian Ridgeback 2021-02-23 17:14:216.2.1 Limiting results
If the whole table is too big and we only want to take a look at the first, say,
10 rows, we can add a LIMIT clause:
## dragon_id sex age_class species update_timestamp
## 1 D1 F Subadult Hebridean Black <NA>
## 2 D2 <NA> Juvenile Romanian Longhorn <NA>
## 3 D3 F Adult Hebridean Black <NA>
## 4 D4 F Adult Peruvian Vipertooth <NA>
## 5 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 6 D6 F Adult Norwegian Ridgeback <NA>
## 7 D7 M Adult Hebridean Black <NA>
## 8 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 9 D9 F Adult Norwegian Ridgeback <NA>
## 10 D10 F Adult Common Welsh Green <NA>6.2.2 Sorting results
One thing to remember with SQL is that the data returned by a SELECT statement
does not necessarily return the data in any specific order unless we tell it to.
You can never assume the output is already sorted. To be explicit about how you
want the data ordered, you can add an ORDER BY clause:
## dragon_id sex age_class species update_timestamp
## 1 D39 <NA> Juvenile Antipodean Opaleye <NA>
## 2 D43 F Subadult Antipodean Opaleye <NA>
## 3 D63 F Adult Antipodean Opaleye <NA>
## 4 D68 M Adult Antipodean Opaleye <NA>
## 5 D74 <NA> Juvenile Antipodean Opaleye <NA>
## 6 D117 <NA> Juvenile Antipodean Opaleye <NA>
## 7 D137 F Adult Antipodean Opaleye <NA>
## 8 D143 F Adult Antipodean Opaleye <NA>
## 9 D153 M Adult Antipodean Opaleye <NA>
## 10 D212 F Adult Antipodean Opaleye <NA>The default ordering will be ascending. If we want descending ordering instead, we can specify that as follows:
## dragon_id sex age_class species update_timestamp
## 1 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 2 D21 F Adult Ukrainian Ironbelly <NA>
## 3 D32 M Adult Ukrainian Ironbelly <NA>
## 4 D35 F Adult Ukrainian Ironbelly <NA>
## 5 D41 <NA> Juvenile Ukrainian Ironbelly <NA>
## 6 D47 F Adult Ukrainian Ironbelly <NA>
## 7 D48 M Adult Ukrainian Ironbelly <NA>
## 8 D66 <NA> Juvenile Ukrainian Ironbelly <NA>
## 9 D122 F Adult Ukrainian Ironbelly <NA>
## 10 D127 M Subadult Ukrainian Ironbelly <NA>6.2.3 Finding unique values
Say that we wanted to know what species of dragons are in the database. We can ask for unique values as follows:
## species
## 1 Hebridean Black
## 2 Romanian Longhorn
## 3 Peruvian Vipertooth
## 4 Ukrainian Ironbelly
## 5 Norwegian Ridgeback
## 6 Common Welsh Green
## 7 Swedish Short-Snout
## 8 Chinese Fireball
## 9 Hungarian Horntail
## 10 Antipodean Opaleye6.2.4 Filtering
We can filter data based on any logical condition using a WHERE clause. For
instance, say that we we only want Norwegian Ridgebacks:
## dragon_id sex age_class species update_timestamp
## 1 D6 F Adult Norwegian Ridgeback <NA>
## 2 D9 F Adult Norwegian Ridgeback <NA>
## 3 D18 F Adult Norwegian Ridgeback <NA>
## 4 D22 <NA> Juvenile Norwegian Ridgeback <NA>
## 5 D27 F Adult Norwegian Ridgeback <NA>
## 6 D29 F Adult Norwegian Ridgeback <NA>
## 7 D34 F Adult Norwegian Ridgeback <NA>
## 8 D51 F Subadult Norwegian Ridgeback <NA>
## 9 D53 <NA> Juvenile Norwegian Ridgeback <NA>
## 10 D54 F Adult Norwegian Ridgeback <NA>We can specify multiple conditions at once. For example, if we want only female Norwegian Ridgebacks:
## dragon_id sex age_class species update_timestamp
## 1 D6 F Adult Norwegian Ridgeback <NA>
## 2 D9 F Adult Norwegian Ridgeback <NA>
## 3 D18 F Adult Norwegian Ridgeback <NA>
## 4 D27 F Adult Norwegian Ridgeback <NA>
## 5 D29 F Adult Norwegian Ridgeback <NA>
## 6 D34 F Adult Norwegian Ridgeback <NA>
## 7 D51 F Subadult Norwegian Ridgeback <NA>
## 8 D54 F Adult Norwegian Ridgeback <NA>
## 9 D56 F Subadult Norwegian Ridgeback <NA>
## 10 D70 F Adult Norwegian Ridgeback <NA>In the example above, both conditions have to be satisfied at once – dragons have to be Norwegian Ridgeback and females to appear in the results. What if we want to return data where at least one of two conditions is satisfied? The following query will return dragons that are either Norwegian Ridgebacks or Peruvian Vipertooths:
SELECT *
FROM dragons
WHERE species = 'Norwegian Ridgeback' OR species = 'Peruvian Vipertooth'
LIMIT 10;## dragon_id sex age_class species update_timestamp
## 1 D4 F Adult Peruvian Vipertooth <NA>
## 2 D6 F Adult Norwegian Ridgeback <NA>
## 3 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 4 D9 F Adult Norwegian Ridgeback <NA>
## 5 D11 F Adult Peruvian Vipertooth <NA>
## 6 D13 <NA> Juvenile Peruvian Vipertooth <NA>
## 7 D17 F Adult Peruvian Vipertooth <NA>
## 8 D18 F Adult Norwegian Ridgeback <NA>
## 9 D22 <NA> Juvenile Norwegian Ridgeback <NA>
## 10 D25 M Adult Peruvian Vipertooth <NA>A more concise way to write the same query would be:
## dragon_id sex age_class species update_timestamp
## 1 D4 F Adult Peruvian Vipertooth <NA>
## 2 D6 F Adult Norwegian Ridgeback <NA>
## 3 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 4 D9 F Adult Norwegian Ridgeback <NA>
## 5 D11 F Adult Peruvian Vipertooth <NA>
## 6 D13 <NA> Juvenile Peruvian Vipertooth <NA>
## 7 D17 F Adult Peruvian Vipertooth <NA>
## 8 D18 F Adult Norwegian Ridgeback <NA>
## 9 D22 <NA> Juvenile Norwegian Ridgeback <NA>
## 10 D25 M Adult Peruvian Vipertooth <NA>Logical conditions also include “greater than”, “less than”, “not equal to”. For instance, we can exclude Norwegian Ridgeback like so:
## dragon_id sex age_class species update_timestamp
## 1 D1 F Subadult Hebridean Black <NA>
## 2 D2 <NA> Juvenile Romanian Longhorn <NA>
## 3 D3 F Adult Hebridean Black <NA>
## 4 D4 F Adult Peruvian Vipertooth <NA>
## 5 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 6 D7 M Adult Hebridean Black <NA>
## 7 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 8 D10 F Adult Common Welsh Green <NA>
## 9 D11 F Adult Peruvian Vipertooth <NA>
## 10 D12 F Adult Swedish Short-Snout <NA>Let’s see some examples with numbers using the morphometrics table. The following query returns any dragons with wingspan greater than 8 meters (incidentally, you can include comments in SQL is by using a double dash):
## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 1 D96 2012-10-10 1069.8965 1389.553
## 2 3 D316 2017-09-08 866.8935 1052.370
## 3 4 D317 2016-09-05 1146.9708 1356.808
## 4 5 D484 2016-12-04 1032.0520 1720.864
## 5 6 D149 2012-02-13 919.9908 1533.599
## 6 9 D283 2007-06-21 1698.1918 1387.194
## 7 11 D485 2002-10-04 957.4830 1780.262
## 8 16 D343 2016-04-08 1520.7012 1537.747
## 9 19 D237 2009-02-22 1204.7588 2120.408
## 10 20 D312 2001-06-16 927.1642 1267.669
## tail_length_cm tarsus_length_cm claw_length_cm
## 1 595.2706 121.65175 15.59622
## 2 373.7619 68.16869 12.71970
## 3 542.5670 172.43663 14.80936
## 4 596.4419 114.05057 11.98567
## 5 563.9201 134.18051 11.00507
## 6 666.4246 147.44219 13.18923
## 7 560.8861 130.86021 16.52066
## 8 618.2842 151.93929 10.37198
## 9 655.5090 134.75780 11.13375
## 10 452.7417 108.84082 11.93288We can also sort the output of the filter:
## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 90 D494 2004-06-12 1307.224 3101.688
## 2 39 D99 2016-11-16 1334.744 2891.525
## 3 86 D378 2013-09-14 1311.868 2792.250
## 4 138 D414 2015-08-28 1721.825 2653.967
## 5 240 D228 2019-06-28 1789.812 2653.470
## 6 312 D476 2000-06-20 1391.101 2617.818
## 7 127 D70 2010-09-10 1601.945 2518.449
## 8 23 D499 2011-12-09 1268.471 2481.832
## 9 282 D496 2006-08-18 1536.888 2460.436
## 10 256 D321 2017-03-19 1423.789 2440.229
## tail_length_cm tarsus_length_cm claw_length_cm
## 1 609.9900 131.2439 14.031487
## 2 596.7174 144.0813 7.619286
## 3 601.6576 107.9930 20.714964
## 4 619.6061 128.5858 18.447108
## 5 604.2838 162.4562 8.846004
## 6 599.2680 138.8046 9.720670
## 7 598.8351 135.7797 8.544782
## 8 609.8503 129.6169 10.313340
## 9 679.7031 136.7213 17.495741
## 10 619.7223 116.3764 7.2667536.2.5 Calculations
The morphometric measurements are in centimeters, but we often define our filtering conditions using meters in our minds (see above, “wingspan greater than 8 meters”). Instead of converting the condition into centimeters, wouldn’t it be easier to have SQLite transform the data in meters and then evaluate the condition? We can do this calculation on the fly:
## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 1 D96 2012-10-10 1069.8965 1389.553
## 2 3 D316 2017-09-08 866.8935 1052.370
## 3 4 D317 2016-09-05 1146.9708 1356.808
## 4 5 D484 2016-12-04 1032.0520 1720.864
## 5 6 D149 2012-02-13 919.9908 1533.599
## 6 9 D283 2007-06-21 1698.1918 1387.194
## 7 11 D485 2002-10-04 957.4830 1780.262
## 8 16 D343 2016-04-08 1520.7012 1537.747
## 9 19 D237 2009-02-22 1204.7588 2120.408
## 10 20 D312 2001-06-16 927.1642 1267.669
## tail_length_cm tarsus_length_cm claw_length_cm
## 1 595.2706 121.65175 15.59622
## 2 373.7619 68.16869 12.71970
## 3 542.5670 172.43663 14.80936
## 4 596.4419 114.05057 11.98567
## 5 563.9201 134.18051 11.00507
## 6 666.4246 147.44219 13.18923
## 7 560.8861 130.86021 16.52066
## 8 618.2842 151.93929 10.37198
## 9 655.5090 134.75780 11.13375
## 10 452.7417 108.84082 11.932886.2.6 Aggregate functions
Summary statistics are calculated using aggregate functions in SQL. Counting, summing, calculating the mean, minimum, maximum values are all examples of aggregate functions. Let’s see how they work.
If we want to know how many Norwegian Ridgebacks are in the database, we can use:
## COUNT(*)
## 1 87The dragons table has no repeated IDs, so we shouldn’t have counted anybody twice. However, let’s double check if that’s true by specifying that we want to only count distinct IDs:
## COUNT(DISTINCT dragon_id)
## 1 87Now let’s see how to calculate some summary stats on dragon morphometrics. What is the mean total body length of dragons in our sample?
## AVG(total_body_length_cm)
## 1 961.3612We can also calculate several different things at once:
SELECT AVG(total_body_length_cm), MIN(total_body_length_cm), MAX(total_body_length_cm)
FROM morphometrics;## AVG(total_body_length_cm) MIN(total_body_length_cm) MAX(total_body_length_cm)
## 1 961.3612 285.6049 2250.7896.2.7 Aliases
Aliases are temporary names that we can assign to a column (or a table) during the execution of a query. For example, we can use an alias to rename the output of our mean body length calculation:
## mean_body_length
## 1 961.36126.2.8 Grouping
If we want to apply the same calculation to different groups within the data,
we can use the GROUP BY clause. GROUP BY is used in conjunction with an
aggregate function to return the computed values broken down by group. For
instance, if we want to count how many dragons we have for each species (and
sort them from the most numerous to the least numerous):
## species n_dragons
## 1 Norwegian Ridgeback 87
## 2 Common Welsh Green 81
## 3 Romanian Longhorn 69
## 4 Hebridean Black 66
## 5 Peruvian Vipertooth 60
## 6 Hungarian Horntail 40
## 7 Swedish Short-Snout 27
## 8 Ukrainian Ironbelly 26
## 9 Antipodean Opaleye 25
## 10 Chinese Fireball 206.2.9 Filtering based on computed values
If we want to apply any filtering to our results based on calculated values, the
WHERE clause is not going to work. Instead, a HAVING clause is used in
combination with an aggregate function and a GROUP BY. HAVING does the same
thing as WHERE except that it handles logical conditions on computed values.
For example, say that we want to count how many individuals we have in our
database and then only keep the species for which we have at least 50 individuals.
The following query counts how many individual dragons we have for each species:
## n_dragons species
## 1 25 Antipodean Opaleye
## 2 20 Chinese Fireball
## 3 81 Common Welsh Green
## 4 66 Hebridean Black
## 5 40 Hungarian Horntail
## 6 87 Norwegian Ridgeback
## 7 60 Peruvian Vipertooth
## 8 69 Romanian Longhorn
## 9 27 Swedish Short-Snout
## 10 26 Ukrainian IronbellyBecause the count is a calculated value (the output of the aggregate function
COUNT), if we try to apply a filter using WHERE we’ll get an error. Instead, we can use HAVING:
SELECT COUNT(DISTINCT dragon_id) AS n_dragons, species
FROM dragons
GROUP BY species
HAVING n_dragons > 50;## n_dragons species
## 1 81 Common Welsh Green
## 2 66 Hebridean Black
## 3 87 Norwegian Ridgeback
## 4 60 Peruvian Vipertooth
## 5 69 Romanian Longhorn6.2.10 Null values
Missing values in SQL are represented as NULL. We can filter (or filter out)
these values using the IS NULL operator:
## dragon_id sex age_class species update_timestamp
## 1 D2 <NA> Juvenile Romanian Longhorn <NA>
## 2 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 3 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 4 D13 <NA> Juvenile Peruvian Vipertooth <NA>
## 5 D14 <NA> Juvenile Hebridean Black <NA>
## 6 D15 <NA> Juvenile Chinese Fireball <NA>
## 7 D22 <NA> Juvenile Norwegian Ridgeback <NA>
## 8 D24 <NA> Juvenile Common Welsh Green <NA>
## 9 D26 <NA> Juvenile Common Welsh Green <NA>
## 10 D31 <NA> Juvenile Common Welsh Green <NA>The query above returns all the dragons for which sex is unknown. If we want to
exclude any individuals for which sex is unknown, then we can add the NOT
operator to our statement:
## dragon_id sex age_class species update_timestamp
## 1 D1 F Subadult Hebridean Black <NA>
## 2 D3 F Adult Hebridean Black <NA>
## 3 D4 F Adult Peruvian Vipertooth <NA>
## 4 D6 F Adult Norwegian Ridgeback <NA>
## 5 D7 M Adult Hebridean Black <NA>
## 6 D9 F Adult Norwegian Ridgeback <NA>
## 7 D10 F Adult Common Welsh Green <NA>
## 8 D11 F Adult Peruvian Vipertooth <NA>
## 9 D12 F Adult Swedish Short-Snout <NA>
## 10 D16 F Adult Chinese Fireball <NA>6.2.11 Joins
So far, we have learned how to query data from a single table. But what if we need to combine information from multiple tables to get the result we want? Let’s make an example. Say that we want to calculate the average wingspan for male versus female dragons. The wingspan measurements are in the morphometrics table. However, the morphometrics table does not have a “sex” column. The information on sex is in the dragons table. To get our answer, we need to combine information from the dragons and morphometrics tables. To do so, we introduce SQL joins.
Joins are the heart of relational database use. Without joins, there is no point in a relational database because we can’t take advantage of the relations between tables. Joins exploit the links we established between tables via foreign keys to combine information across them.
There are several types of join. The most common types are left join, inner join, or full join. To understand this terminology, consider this: whenever you are joining two tables, the first table you mention (the one to which you’re joining) is called the left table, whereas the second table (the one you’re joining to the first) is called the right table. With a left join, you keep all the records in the left table and add information from the right table whenever there’s a matching row. A full join means that you retain all rows from both tables, matching them whenever possible. An inner join means that you only retain the rows that match between the two tables.
Figure 6.1: SQL Joins
Let’s look at this in practice and it will make more sense. Our database contains a deployments table and a morphometrics table. Not all dragons that were tracked were also measured. If we do a left join using the deployments as the left table, we get in output the whole deployments table (all the dragons that were tracked) with the associated morphometric information whenever available (for the dragons that were also measured):
SELECT *
FROM deployments -- this is our left table
LEFT JOIN morphometrics -- this is our right table
ON deployments.dragon_id = morphometrics.dragon_id -- this is the shared column
LIMIT 10;## deployment_id dragon_id tag_id start_deployment end_deployment
## 1 1 D486 N33529 2006-12-20 2007-07-04
## 2 2 D393 J47978 2008-01-13 2008-10-13
## 3 3 D88 R61684 2004-09-19 2004-12-01
## 4 4 D330 B35524 2015-11-21 2016-08-02
## 5 5 D478 T55954 2002-05-07 2002-10-26
## 6 6 D300 O31688 2006-01-20 2006-08-23
## 7 7 D380 B61925 2015-01-27 2015-10-21
## 8 8 D315 P47677 2006-03-03 2006-06-06
## 9 9 D209 P35987 2007-02-26 2007-05-31
## 10 10 D357 I41609 2013-09-09 2014-03-08
## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 14 D486 2006-12-20 315.2255 616.5057
## 2 146 D393 2008-01-13 1275.6809 803.7776
## 3 NA <NA> <NA> NA NA
## 4 252 D330 2015-11-21 1364.8418 1351.6375
## 5 NA <NA> <NA> NA NA
## 6 NA <NA> <NA> NA NA
## 7 260 D380 2015-01-27 327.5435 616.5409
## 8 NA <NA> <NA> NA NA
## 9 82 D209 2007-02-26 325.2996 670.5136
## 10 31 D357 2013-09-09 730.9783 972.8464
## tail_length_cm tarsus_length_cm claw_length_cm
## 1 117.3121 31.70299 4.980824
## 2 638.4500 133.38012 12.472582
## 3 NA NA NA
## 4 637.7992 140.29208 14.076526
## 5 NA NA NA
## 6 NA NA NA
## 7 102.2240 35.78315 4.716980
## 8 NA NA NA
## 9 118.8795 41.10574 4.926693
## 10 489.0859 93.98672 17.895960Since the shared column is named the same in the two tables (dragon_id), I had
to specify which table I was referring to each time in the ON clause, or it
would have been ambiguous. The syntax to do so is table.column. Also note that,
because the dragon ID column appears in both tables and we did not specify which
table we wanted it from, SQLite is duplicating it. To avoid that, we need to get
rid of the wildcard and spell out the name of each of the columns we want in
output (also specifying the table when ambiguous):
SELECT deployments.dragon_id, date, tag_id, start_deployment, end_deployment,
total_body_length_cm, wingspan_cm, tail_length_cm, tarsus_length_cm, claw_length_cm
FROM deployments
LEFT JOIN morphometrics
ON deployments.dragon_id = morphometrics.dragon_id
LIMIT 10;## dragon_id date tag_id start_deployment end_deployment
## 1 D486 2006-12-20 N33529 2006-12-20 2007-07-04
## 2 D393 2008-01-13 J47978 2008-01-13 2008-10-13
## 3 D88 <NA> R61684 2004-09-19 2004-12-01
## 4 D330 2015-11-21 B35524 2015-11-21 2016-08-02
## 5 D478 <NA> T55954 2002-05-07 2002-10-26
## 6 D300 <NA> O31688 2006-01-20 2006-08-23
## 7 D380 2015-01-27 B61925 2015-01-27 2015-10-21
## 8 D315 <NA> P47677 2006-03-03 2006-06-06
## 9 D209 2007-02-26 P35987 2007-02-26 2007-05-31
## 10 D357 2013-09-09 I41609 2013-09-09 2014-03-08
## total_body_length_cm wingspan_cm tail_length_cm tarsus_length_cm
## 1 315.2255 616.5057 117.3121 31.70299
## 2 1275.6809 803.7776 638.4500 133.38012
## 3 NA NA NA NA
## 4 1364.8418 1351.6375 637.7992 140.29208
## 5 NA NA NA NA
## 6 NA NA NA NA
## 7 327.5435 616.5409 102.2240 35.78315
## 8 NA NA NA NA
## 9 325.2996 670.5136 118.8795 41.10574
## 10 730.9783 972.8464 489.0859 93.98672
## claw_length_cm
## 1 4.980824
## 2 12.472582
## 3 NA
## 4 14.076526
## 5 NA
## 6 NA
## 7 4.716980
## 8 NA
## 9 4.926693
## 10 17.895960If we invert the tables (the morphometrics becomes the left table and the deployments becomes the right), we get in output the whole morphometric table (all the dragons that were measured) with the associated deployment information whenever available (for the dragons that were also tracked):
SELECT *
FROM morphometrics -- this is our left table
LEFT JOIN deployments -- this is our right table
ON morphometrics.dragon_id = deployments.dragon_id
LIMIT 10;## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 1 D96 2012-10-10 1069.8965 1389.5527
## 2 2 D400 2003-07-03 333.4600 634.9109
## 3 3 D316 2017-09-08 866.8935 1052.3702
## 4 4 D317 2016-09-05 1146.9708 1356.8084
## 5 5 D484 2016-12-04 1032.0520 1720.8641
## 6 6 D149 2012-02-13 919.9908 1533.5991
## 7 7 D285 2016-03-23 304.8285 698.8157
## 8 8 D256 2013-09-07 358.9701 652.0053
## 9 9 D283 2007-06-21 1698.1918 1387.1943
## 10 10 D213 2001-12-12 353.6952 670.5283
## tail_length_cm tarsus_length_cm claw_length_cm deployment_id dragon_id
## 1 595.2706 121.65175 15.596219 274 D96
## 2 104.2241 38.10844 4.305086 260 D400
## 3 373.7619 68.16869 12.719697 NA <NA>
## 4 542.5670 172.43663 14.809363 98 D317
## 5 596.4419 114.05057 11.985672 285 D484
## 6 563.9201 134.18051 11.005070 NA <NA>
## 7 115.8964 42.18657 5.041634 126 D285
## 8 148.3656 43.57849 4.576640 291 D256
## 9 666.4246 147.44219 13.189233 145 D283
## 10 140.4342 43.60513 4.248564 128 D213
## tag_id start_deployment end_deployment
## 1 H83101 2012-10-10 2013-06-02
## 2 S49621 2003-07-03 2004-01-17
## 3 <NA> <NA> <NA>
## 4 A49007 2016-09-05 2017-01-09
## 5 V63425 2016-12-04 2017-02-19
## 6 <NA> <NA> <NA>
## 7 B74989 2016-03-23 2016-11-08
## 8 O66678 2013-09-07 2013-11-10
## 9 G59298 2007-06-21 2007-11-14
## 10 F64333 2001-12-12 2002-02-05An inner join only keeps the rows that match between two tables. In this case, that means we only get in output data for animals that were both tracked and measured:
SELECT *
FROM morphometrics
INNER JOIN deployments
ON morphometrics.dragon_id = deployments.dragon_id
LIMIT 10;## measurement_id dragon_id date total_body_length_cm wingspan_cm
## 1 1 D96 2012-10-10 1069.8965 1389.5527
## 2 2 D400 2003-07-03 333.4600 634.9109
## 3 4 D317 2016-09-05 1146.9708 1356.8084
## 4 5 D484 2016-12-04 1032.0520 1720.8641
## 5 7 D285 2016-03-23 304.8285 698.8157
## 6 8 D256 2013-09-07 358.9701 652.0053
## 7 9 D283 2007-06-21 1698.1918 1387.1943
## 8 10 D213 2001-12-12 353.6952 670.5283
## 9 13 D41 2016-11-03 325.5946 626.2576
## 10 14 D486 2006-12-20 315.2255 616.5057
## tail_length_cm tarsus_length_cm claw_length_cm deployment_id dragon_id
## 1 595.27056 121.65175 15.596219 274 D96
## 2 104.22414 38.10844 4.305086 260 D400
## 3 542.56700 172.43663 14.809363 98 D317
## 4 596.44195 114.05057 11.985672 285 D484
## 5 115.89640 42.18657 5.041634 126 D285
## 6 148.36555 43.57849 4.576640 291 D256
## 7 666.42455 147.44219 13.189233 145 D283
## 8 140.43424 43.60513 4.248564 128 D213
## 9 86.63968 39.26696 6.077829 114 D41
## 10 117.31209 31.70299 4.980824 1 D486
## tag_id start_deployment end_deployment
## 1 H83101 2012-10-10 2013-06-02
## 2 S49621 2003-07-03 2004-01-17
## 3 A49007 2016-09-05 2017-01-09
## 4 V63425 2016-12-04 2017-02-19
## 5 B74989 2016-03-23 2016-11-08
## 6 O66678 2013-09-07 2013-11-10
## 7 G59298 2007-06-21 2007-11-14
## 8 F64333 2001-12-12 2002-02-05
## 9 X71699 2016-11-03 2017-05-10
## 10 N33529 2006-12-20 2007-07-04A full join keeps all records from both the left and the right table, matching them whenever possible. That is, we get in output all the dragons, with blanks in the morphometrics table for those that were only tracked and blanks in the deployments table for those that were only measured. Unfortunately, SQLite does not support full joins, so we cannot demonstrate it here, but it’s important to know that a full join exists and what it does because you’ll find yourself using it in any other database management program or even in R (see Chapter 13).
6.2.12 Nested SELECT statements
Now that we know how to use joins, we can go back to our challenge of calculating the average wingspan for male versus female dragons. What we need to do is add the sex column to the morphometrics table. We can do this by looking at the dragon ID, which is the column the two tables have in common. So the join clause will look like this:
SELECT morphometrics.dragon_id, wingspan_cm, sex
FROM morphometrics -- this is our left table
LEFT JOIN dragons -- this is our left table
ON morphometrics.dragon_id = dragons.dragon_id -- this is the shared column
LIMIT 10;## dragon_id wingspan_cm sex
## 1 D96 1389.5527 F
## 2 D400 634.9109 <NA>
## 3 D316 1052.3702 M
## 4 D317 1356.8084 F
## 5 D484 1720.8641 M
## 6 D149 1533.5991 M
## 7 D285 698.8157 <NA>
## 8 D256 652.0053 <NA>
## 9 D283 1387.1943 F
## 10 D213 670.5283 <NA>By using a left join, we are saying that we want to keep all rows from the left table (morphometrics) while adding information on sex whenever available. Now we can compute the average wingspan broken down by sex:
SELECT sex, AVG(wingspan_cm) AS mean_wingspan
FROM (
SELECT morphometrics.dragon_id, wingspan_cm, sex
FROM morphometrics
LEFT JOIN dragons
ON morphometrics.dragon_id = dragons.dragon_id
)
GROUP BY sex; ## sex mean_wingspan
## 1 <NA> 645.3158
## 2 F 1550.0009
## 3 M 1549.1300The one above is a nested query, which means there are two SELECT statements
nested within one another. The inner SELECT statement (everything between the
parentheses) is treated as if it were a table in the database. SQL will
execute the query from the inside out, so even though that table physically does
not exist, it gets temporarily created when the inner query is run and is then
used in input to the second query.
6.2.13 Order of operations
The fact that SQL will execute nested queries from the inside out is one aspect of order of operations. But there’s also a logic to the order in which SQL executes clauses within a query: first, it gathers the data, then it filters it and aggregates it as needed, then it computes results, and finally it sorts them and truncate them if necessary. Let’s look at this step by step:
- First, SQL executes the
FROMclause and anyJOINclauses, if present, to determine what tables are being queried. - Then, it will execute the
WHEREclause to filter the data. - Then, it will
GROUP BYthe column/s of interest. - Then it will calculate any derived values based on aggregate functions.
- Then, it will apply any filters specified by
HAVING. - Now, and only now, it will execute the
SELECTclause! - Once the computations are completed and the output of
SELECTis ready, SQL can start refining it. First, it will discard any duplicates ifDISTINCTis specified. - Then, it will sort the results based on
ORDER BY. - Finally, it will truncate the output if a
LIMITis specified.
If you think about it, all of this makes logical sense. You can’t select a
column if you’re not sure what table to look in. You can’t compute a per-group
count before defining the groups. You can’t order results that you haven’t
computed yet. But then why do we start our queries with SELECT? And does the
order in which we write our queries matter?
The answer to both of those questions is that there is a difference between the logical order of operations and the lexical (or syntactical) order of operations, which is how we actually write queries. Even though these don’t correspond, writing a query in any other order than the following is incorrect (and will return an error):
6.3 Building a database
6.3.1 Creating a new database in SQLite Studio
We are now going to see how to build a database by recreating the dragons database we have been practicing on. Let’s open up SQLite Studio and, on the Database tab, click “Add a database” (or use Ctrl/Cmd + O as a shortcut). Click on the green plus sign, navigate to the folder where you want to save the database, and choose a file name. Click “Save”. Now we need to also choose a name to use internally (this name will appear in the drop-down list of databases within SQLite, but it does not necessarily need to be the same as the filename.) Click “OK” and you should see your new database in the list on the left.
6.3.2 Creating tables
Now let’s open the SQL editor (Tools > SQL editor). Double check that you are working on the correct database (the name of the active database is shown in the toolbar). We are ready to create our first table!
To create a table, we need to specify a name for the table, as well as a name and a data type for each column. The basic format is as follows:
Let’s start by creating the dragons table. Remember that each table needs to have a primary key, i.e., a column that serves as the unique identifier of each row. The values in this column need to be unique and cannot be null. In this table, we can use the dragon ID as the primary key:
CREATE TABLE dragons (
dragon_id varchar(5),
sex char(1),
age_class varchar(8),
species varchar(50),
PRIMARY KEY (dragon_id)
);Notice that I specified a number of digits for each character variable. Because the format of the dragon ID is “D” + number from 1 up to 500 (for now), setting the ID as a character string with varying size up to 5 digits allows for IDs from “D1” to “D9999”. So far, we only have 500 individuals, so strictly it would have been enough to set the limit to 4 digits only, but it’s good to have some forethought and allow for growth into the future. At the same time, it seems reasonable to assume we won’t catch 10 thousand dragons in this project, so 5 digits is a good compromise. In reality, space is rarely limiting to the point where 4 or 10 digits makes a difference, so when in doubt err on the side of more room for growth.
While dragon ID, age class, and species have a variable number of digits, sex
always has one (it can be “M” or “F”). So we can make this a char instead of
a varchar and specify it will have 1 digit.
6.3.3 Adding constraints
We can also add some constraints for the purpose of quality assurance. For example, because the dragon ID is the primary key, we can’t accept null values in this column. Sex is always one of “M” or “F” and age is always one of “Juvenile”, “Subadult”, or “Adult”. In other SQL dialects you can add these after the fact, but in SQLite the only way to add these constraints is at the same time as you create the table. We can delete the table and re-create it by modifying the above syntax as follows:
6.3.4 Order of table creation
Foreign keys are also specified as constraints. Because it’s not possible to enforce constraints as an afterthought, we need to plan the order in which we add tables carefully. If we try to add a foreign key that refers to a table that doesn’t exist yet, we won’t be able to. Let’s take another look at the diagram of our table relationships:
Figure 6.2: Diagram of the dragons database
Any table that has one or more foreign keys needs to be added after the related table/s. In our case, there are three “root” tables that do not have any foreign keys: the dragons table, the tags table, and the capture sites table. We can add these three first and then all the others.
The tags table has a tag_id field which is unique and can therefore be used as
a primary key. Note that when you make a column the primary key you automatically
enforce a unique constraint on that column. However, SQLite does not enforce a
not-null constraint on primary keys like most other SQL dialects. Because SQLite
doesn’t, we have to do it ourselves:
The capture sites table has a site field which contains a 3-letter code that
uniquely identifies the site. We can use that as a primary key. The UTM
coordinates are numeric values for which we can use the data type called “double
precision”, or just “double”. There are several possible choices for numeric
data types. “Double precision” and “float” are both suitable data types for
storing real numbers, but double precision stores numeric values
with higher precision than float. Both of these allow for variable decimal
places, whereas the data type “decimal” enforces the same number of decimal
places across records. The choice between these data types depends on 1. whether
we want the measurements to all have the same number of decimal places or not,
and 2. how many significant digits do we expect/care about. Double precision can
store up to 15 significant digits (unlike float which can store up to 8), but it
also occupies double the space (64 bit instead of 32.) For UTM coordinates, the
Y value has a minimum of 7 digits, and we want to keep decimal places because
we need the highest precision possible on the position of animals in space.
Therefore, we’ll go with double precision:
Note that I used an alternative syntax to specify the primary key. This is equivalent to the one I used above for the dragons table.
6.3.5 Populating the tables
Now that we added a few tables, we can start to populate the database by loading the data as .csv files. On the Tools tab, click “Import.”
Check that the database is correct and then select the table you want to import data into. For example, let’s start with the dragons table:
Click Next. Now, browse your directory to select the input file. Then check
the box that says “First line represents CSV column names”, make sure the field
separator is a comma, and set the NULL values to NA (which is how they are
encoded in the .csv.) Click Finish.
To check if the table was imported correctly, go back into the query editor and try to look at the first 10 rows:
## dragon_id sex age_class species update_timestamp
## 1 D1 F Subadult Hebridean Black <NA>
## 2 D2 <NA> Juvenile Romanian Longhorn <NA>
## 3 D3 F Adult Hebridean Black <NA>
## 4 D4 F Adult Peruvian Vipertooth <NA>
## 5 D5 <NA> Juvenile Ukrainian Ironbelly <NA>
## 6 D6 F Adult Norwegian Ridgeback <NA>
## 7 D7 M Adult Hebridean Black <NA>
## 8 D8 <NA> Juvenile Peruvian Vipertooth <NA>
## 9 D9 F Adult Norwegian Ridgeback <NA>
## 10 D10 F Adult Common Welsh Green <NA>If everything looks good, we can go ahead and import data in the other two tables.
6.3.6 Autoincrements as primary keys
Sometimes a table does not contain any columns with unique values. This is the case for all the tables we have left to add. What do we use as primary key in these situations? Adding a column with a serial number that gets automatically updated is a good option. SQLite has something called auto-increment, which is an integer column that automatically increases by 1 each time you add a row to a table. Because it’s incremental, the values of an auto-increment will always be unique, and because it’s automatic, they will never be null. Sounds like a perfect candidate for a primary key.
The problem with using an auto-increment as a primary key arises when you’re trying to import data from a .csv file. If the column with the auto-increment does not already exist in the .csv, SQLite won’t let you import the file into the table because the number of columns does not match. We don’t want to add the auto-increment into the .csv ourselves because that defeats the purpose of having SQLite doing it for us. But if we import the .csv as it is (without primary key) and then add the auto-increment column later, we won’t be able to make it the primary key because SQLite won’t let us. So, what do we do?
One workaround that people have found to solve this issue is to trick SQLite by using a temporary table. This is how the process works:
- Create the table the way we want it, with an auto-increment primary key plus all the columns we want to import from the .csv;
- Create a temporary table without primary key that only contains the columns from the .csv;
- Import the .csv into the temporary table;
- Populate the final table by pulling data from the temporary table;
- Delete the temporary table.
A little convoluted, but it does the job. Let’s demonstrate this on the captures table. First, we create the table like we want it to look in the end (note that I am adding foreign keys; we’ll go over that part in the next section):
CREATE TABLE captures (
capture_id INTEGER PRIMARY KEY AUTOINCREMENT,
dragon_id varchar(5),
date text,
site char(3),
FOREIGN KEY(dragon_id) REFERENCES dragons(dragon_id)
FOREIGN KEY(site) REFERENCES capture_sites(site)
);Second, we create a temporary table without the primary key (no need to add foreign keys to this one as we are going to delete it anyway):
Now on Tools > Import, we upload captures.csv into captures_temp. Then
we can populate the final table as follows:
And finally we delete our temporary table:
We better get familiar with this workflow because we are going to use it for all the other tables now.
6.3.7 Foreign keys
For each of the remaining tables, we will specify one or more foreign keys to
enforce the relationships between tables. Each foreign key is the primary key of
another table. See for example what we did above: the captures table we just
imported contains information on when and where each dragon was captured. This
means this table needs to have two foreign keys: the dragon_id column links it
to the dragons table and the site column links it to the capture sites table.
Now let’s apply the concept to the other tables.
The morphometrics table will have a single foreign key linking it to the dragons table (the dragon ID). The second column is a date – SQLite does not have a dedicated data type for dates. Instead, we stored this as a character string in ISO8601 format (“YYYY-MM-DD HH:MM:SS.SSS”). This time there is no need for double precision because we want to only retain up to the third decimal place and the numbers are not larger than ~3000, so 8 significant digits is sufficient. We’ll use float as the data type for the measurements. Because individuals may have been measured multiple times, none of the existing columns are unique. This means we’ll create a serial number to use as the primary key. We’ll use the same trick as above:
CREATE TABLE morphometrics (
measurement_id INTEGER PRIMARY KEY AUTOINCREMENT,
dragon_id varchar(5),
date text,
total_body_length_cm float,
wingspan_cm float,
tail_length_cm float,
tarsus_length_cm float,
claw_length_cm float,
FOREIGN KEY (dragon_id) REFERENCES dragons(dragon_id)
);
CREATE TABLE morphometrics_temp (
dragon_id varchar(5),
date text,
total_body_length_cm float,
wingspan_cm float,
tail_length_cm float,
tarsus_length_cm float,
claw_length_cm float
);Now on Tools > Import, we upload morphometrics.csv into
morphometrics_temp. Then we populate the final table:
INSERT INTO morphometrics(dragon_id, date, total_body_length_cm, wingspan_cm,
tail_length_cm, tarsus_length_cm, claw_length_cm)
SELECT * FROM morphometrics_temp;And delete our temporary table:
The diet table contains repeated sample IDs and repeated item IDs within each sample. We’ll need a serial number here too because none of the columns are unique. The item ID is an integer so we are going to use a new numeric data type for it. The foreign key will be, again, the dragon ID referring to the dragons table:
CREATE TABLE diet (
diet_id INTEGER PRIMARY KEY AUTOINCREMENT,
dragon_id varchar(5),
sample_id varchar(8),
date text,
item_id integer,
item varchar(50),
FOREIGN KEY (dragon_id) REFERENCES dragons(dragon_id)
);
CREATE TABLE diet_temp (
dragon_id varchar(5),
sample_id varchar(8),
date text,
item_id integer,
item varchar(50)
);Upload diet.csv into diet_temp.
INSERT INTO diet(dragon_id, sample_id, date, item_id, item)
SELECT * FROM diet_temp;
DROP TABLE diet_temp;The deployments table assigns a tag to each individual within a certain period
of time. The dragon_id column will be the foreign key that links it to the
dragons table, and the tag_id column will link it to the tags table. The start
and end deployment dates will be stored as ISO8601 text. Again, we’ll need a
serial number to use as a primary key:
CREATE TABLE deployments (
deployment_id INTEGER PRIMARY KEY AUTOINCREMENT,
dragon_id varchar(5),
tag_id char(6),
start_deployment text,
end_deployment text,
FOREIGN KEY(dragon_id) REFERENCES dragons(dragon_id)
FOREIGN KEY(tag_id) REFERENCES tags(tag_id)
);
CREATE TABLE deployments_temp (
dragon_id varchar(5),
tag_id char(6),
start_deployment text,
end_deployment text
);Upload deployments.csv into deployments_temp.
INSERT INTO deployments(dragon_id, tag_id, start_deployment, end_deployment)
SELECT * FROM deployments_temp;
DROP TABLE deployments_temp;Now we can input the telemetry data. This table contains the raw tracking data as we download it from the tags. We’ll need a serial number to uniquely identify each record, and we’ll add the tag ID as the foreign key to the tags table:
CREATE TABLE gps_data_raw (
gps_id INTEGER PRIMARY KEY AUTOINCREMENT,
tag_id char(6),
timestamp text,
utm_x double,
utm_y double,
FOREIGN KEY(tag_id) REFERENCES tags(tag_id)
);
CREATE TABLE gps_data_raw_temp (
tag_id char(6),
timestamp text,
utm_x double,
utm_y double
);Upload telemetry_raw.csv into gps_data_raw_temp.
6.3.8 Crossing existing information to derive new tables
The raw GPS data table does not give us any information about which animal each location corresponds to; all we know is the tag ID. Each tag does not correspond to an individual, because some tags are reused on multiple dragons. So how do we make these data usable? How do we know who is who? To associate each location to the correct animal, we need to know who was wearing the tag at the time that location was taken. There is a very elegant solution to our problem, as we can pull the range of dates an individual was wearing a certain tag from the deployments table, cross those dates with the dates in the raw GPS data, and create an updated telemetry table where each location is assigned to the correct individual. No manual work involved. Are you ready for some magic?! First, we create the table structure:
CREATE TABLE gps_data (
loc_id INTEGER PRIMARY KEY,
tag_id char(6),
dragon_id varchar(5),
timestamp text,
utm_x double,
utm_y double,
FOREIGN KEY (tag_id) REFERENCES tags(tag_id)
FOREIGN KEY (dragon_id) REFERENCES dragons(dragon_id)
);And then we populate it by pulling information from the raw GPS and deployment
tables. Locations are assigned to the individual that was wearing the tag at the
time based on the WHERE clause:
INSERT INTO gps_data (
tag_id, dragon_id, timestamp, utm_x, utm_y)
SELECT
deployments.tag_id,
deployments.dragon_id,
gps_data_raw.timestamp,
gps_data_raw.utm_x,
gps_data_raw.utm_y
FROM deployments LEFT JOIN gps_data_raw USING (tag_id)
WHERE gps_data_raw.tag_id = deployments.tag_id AND
(
(
(strftime(gps_data_raw.timestamp) >= strftime(deployments.start_deployment)) AND
(strftime(gps_data_raw.timestamp) <= strftime(deployments.end_deployment))
)
OR
(
(gps_data_raw.timestamp >= deployments.start_deployment) AND
(deployments.end_deployment IS NULL)
)
);Note that, because we populated this table with data from other existing tables,
we ended up using INSERT INTO anyway and there was no need to use our trick
with a temporary table.
It should now be apparent that keeping the deployments table correctly filled out with no gaps or errors is of vital importance for the integrity of the whole telemetry database. Having the database set up this way means we never have to manually assign locations to animals, which would for sure lead to errors, but it also means that any analysis downstream hinges on keeping the deployments table up-to-date with new captures, tag retrievals, and deaths. This is just one example of how databases can save us time and ensure data integrity with minimal routine effort, but only if the data is curated with care in the first place.