Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * windowfuncs.c
4 : * Standard window functions defined in SQL spec.
5 : *
6 : * Portions Copyright (c) 2000-2024, PostgreSQL Global Development Group
7 : *
8 : *
9 : * IDENTIFICATION
10 : * src/backend/utils/adt/windowfuncs.c
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 : #include "postgres.h"
15 :
16 : #include "nodes/parsenodes.h"
17 : #include "nodes/supportnodes.h"
18 : #include "utils/fmgrprotos.h"
19 : #include "windowapi.h"
20 :
21 : /*
22 : * ranking process information
23 : */
24 : typedef struct rank_context
25 : {
26 : int64 rank; /* current rank */
27 : } rank_context;
28 :
29 : /*
30 : * ntile process information
31 : */
32 : typedef struct
33 : {
34 : int32 ntile; /* current result */
35 : int64 rows_per_bucket; /* row number of current bucket */
36 : int64 boundary; /* how many rows should be in the bucket */
37 : int64 remainder; /* (total rows) % (bucket num) */
38 : } ntile_context;
39 :
40 : static bool rank_up(WindowObject winobj);
41 : static Datum leadlag_common(FunctionCallInfo fcinfo,
42 : bool forward, bool withoffset, bool withdefault);
43 :
44 :
45 : /*
46 : * utility routine for *_rank functions.
47 : */
48 : static bool
49 165678 : rank_up(WindowObject winobj)
50 : {
51 165678 : bool up = false; /* should rank increase? */
52 165678 : int64 curpos = WinGetCurrentPosition(winobj);
53 : rank_context *context;
54 :
55 : context = (rank_context *)
56 165678 : WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
57 :
58 165678 : if (context->rank == 0)
59 : {
60 : /* first call: rank of first row is always 1 */
61 : Assert(curpos == 0);
62 408 : context->rank = 1;
63 : }
64 : else
65 : {
66 : Assert(curpos > 0);
67 : /* do current and prior tuples match by ORDER BY clause? */
68 165270 : if (!WinRowsArePeers(winobj, curpos - 1, curpos))
69 134250 : up = true;
70 : }
71 :
72 : /* We can advance the mark, but only *after* access to prior row */
73 165678 : WinSetMarkPosition(winobj, curpos);
74 :
75 165678 : return up;
76 : }
77 :
78 :
79 : /*
80 : * row_number
81 : * just increment up from 1 until current partition finishes.
82 : */
83 : Datum
84 457656 : window_row_number(PG_FUNCTION_ARGS)
85 : {
86 457656 : WindowObject winobj = PG_WINDOW_OBJECT();
87 457656 : int64 curpos = WinGetCurrentPosition(winobj);
88 :
89 457656 : WinSetMarkPosition(winobj, curpos);
90 457656 : PG_RETURN_INT64(curpos + 1);
91 : }
92 :
93 : /*
94 : * window_row_number_support
95 : * prosupport function for window_row_number()
96 : */
97 : Datum
98 654 : window_row_number_support(PG_FUNCTION_ARGS)
99 : {
100 654 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
101 :
102 654 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
103 : {
104 54 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
105 :
106 : /* row_number() is monotonically increasing */
107 54 : req->monotonic = MONOTONICFUNC_INCREASING;
108 54 : PG_RETURN_POINTER(req);
109 : }
110 :
111 600 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
112 : {
113 288 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
114 :
115 : /*
116 : * The frame options can always become "ROWS BETWEEN UNBOUNDED
117 : * PRECEDING AND CURRENT ROW". row_number() always just increments by
118 : * 1 with each row in the partition. Using ROWS instead of RANGE
119 : * saves effort checking peer rows during execution.
120 : */
121 288 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
122 : FRAMEOPTION_ROWS |
123 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
124 : FRAMEOPTION_END_CURRENT_ROW);
125 :
126 288 : PG_RETURN_POINTER(req);
127 : }
128 :
129 312 : PG_RETURN_POINTER(NULL);
130 : }
131 :
132 : /*
133 : * rank
134 : * Rank changes when key columns change.
135 : * The new rank number is the current row number.
136 : */
137 : Datum
138 165486 : window_rank(PG_FUNCTION_ARGS)
139 : {
140 165486 : WindowObject winobj = PG_WINDOW_OBJECT();
141 : rank_context *context;
142 : bool up;
143 :
144 165486 : up = rank_up(winobj);
145 : context = (rank_context *)
146 165486 : WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
147 165486 : if (up)
148 134172 : context->rank = WinGetCurrentPosition(winobj) + 1;
149 :
150 165486 : PG_RETURN_INT64(context->rank);
151 : }
152 :
153 : /*
154 : * window_rank_support
155 : * prosupport function for window_rank()
156 : */
157 : Datum
158 354 : window_rank_support(PG_FUNCTION_ARGS)
159 : {
160 354 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
161 :
162 354 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
163 : {
164 12 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
165 :
166 : /* rank() is monotonically increasing */
167 12 : req->monotonic = MONOTONICFUNC_INCREASING;
168 12 : PG_RETURN_POINTER(req);
169 : }
170 :
171 342 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
172 : {
173 150 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
174 :
175 : /*
176 : * rank() is coded in such a way that it returns "(COUNT (*) OVER
177 : * (<opt> RANGE UNBOUNDED PRECEDING) - COUNT (*) OVER (<opt> RANGE
178 : * CURRENT ROW) + 1)" regardless of the frame options. We'll set the
179 : * frame options to "ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW"
180 : * so they agree with what window_row_number_support() optimized the
181 : * frame options to be. Using ROWS instead of RANGE saves from doing
182 : * peer row checks during execution.
183 : */
184 150 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
185 : FRAMEOPTION_ROWS |
186 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
187 : FRAMEOPTION_END_CURRENT_ROW);
188 :
189 150 : PG_RETURN_POINTER(req);
190 : }
191 :
192 192 : PG_RETURN_POINTER(NULL);
193 : }
194 :
195 : /*
196 : * dense_rank
197 : * Rank increases by 1 when key columns change.
198 : */
199 : Datum
200 72 : window_dense_rank(PG_FUNCTION_ARGS)
201 : {
202 72 : WindowObject winobj = PG_WINDOW_OBJECT();
203 : rank_context *context;
204 : bool up;
205 :
206 72 : up = rank_up(winobj);
207 : context = (rank_context *)
208 72 : WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
209 72 : if (up)
210 30 : context->rank++;
211 :
212 72 : PG_RETURN_INT64(context->rank);
213 : }
214 :
215 : /*
216 : * window_dense_rank_support
217 : * prosupport function for window_dense_rank()
218 : */
219 : Datum
220 72 : window_dense_rank_support(PG_FUNCTION_ARGS)
221 : {
222 72 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
223 :
224 72 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
225 : {
226 18 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
227 :
228 : /* dense_rank() is monotonically increasing */
229 18 : req->monotonic = MONOTONICFUNC_INCREASING;
230 18 : PG_RETURN_POINTER(req);
231 : }
232 :
233 54 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
234 : {
235 24 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
236 :
237 : /*
238 : * dense_rank() is unaffected by the frame options. Here we set the
239 : * frame options to match what's done in row_number's support
240 : * function. Using ROWS instead of RANGE (the default) saves the
241 : * executor from having to check for peer rows.
242 : */
243 24 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
244 : FRAMEOPTION_ROWS |
245 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
246 : FRAMEOPTION_END_CURRENT_ROW);
247 :
248 24 : PG_RETURN_POINTER(req);
249 : }
250 :
251 30 : PG_RETURN_POINTER(NULL);
252 : }
253 :
254 : /*
255 : * percent_rank
256 : * return fraction between 0 and 1 inclusive,
257 : * which is described as (RK - 1) / (NR - 1), where RK is the current row's
258 : * rank and NR is the total number of rows, per spec.
259 : */
260 : Datum
261 60 : window_percent_rank(PG_FUNCTION_ARGS)
262 : {
263 60 : WindowObject winobj = PG_WINDOW_OBJECT();
264 : rank_context *context;
265 : bool up;
266 60 : int64 totalrows = WinGetPartitionRowCount(winobj);
267 :
268 : Assert(totalrows > 0);
269 :
270 60 : up = rank_up(winobj);
271 : context = (rank_context *)
272 60 : WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
273 60 : if (up)
274 24 : context->rank = WinGetCurrentPosition(winobj) + 1;
275 :
276 : /* return zero if there's only one row, per spec */
277 60 : if (totalrows <= 1)
278 6 : PG_RETURN_FLOAT8(0.0);
279 :
280 54 : PG_RETURN_FLOAT8((float8) (context->rank - 1) / (float8) (totalrows - 1));
281 : }
282 :
283 : /*
284 : * window_percent_rank_support
285 : * prosupport function for window_percent_rank()
286 : */
287 : Datum
288 24 : window_percent_rank_support(PG_FUNCTION_ARGS)
289 : {
290 24 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
291 :
292 24 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
293 : {
294 0 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
295 :
296 : /* percent_rank() is monotonically increasing */
297 0 : req->monotonic = MONOTONICFUNC_INCREASING;
298 0 : PG_RETURN_POINTER(req);
299 : }
300 :
301 24 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
302 : {
303 12 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
304 :
305 : /*
306 : * percent_rank() is unaffected by the frame options. Here we set the
307 : * frame options to match what's done in row_number's support
308 : * function. Using ROWS instead of RANGE (the default) saves the
309 : * executor from having to check for peer rows.
310 : */
311 12 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
312 : FRAMEOPTION_ROWS |
313 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
314 : FRAMEOPTION_END_CURRENT_ROW);
315 :
316 12 : PG_RETURN_POINTER(req);
317 : }
318 :
319 12 : PG_RETURN_POINTER(NULL);
320 : }
321 :
322 :
323 : /*
324 : * cume_dist
325 : * return fraction between 0 and 1 inclusive,
326 : * which is described as NP / NR, where NP is the number of rows preceding or
327 : * peers to the current row, and NR is the total number of rows, per spec.
328 : */
329 : Datum
330 60 : window_cume_dist(PG_FUNCTION_ARGS)
331 : {
332 60 : WindowObject winobj = PG_WINDOW_OBJECT();
333 : rank_context *context;
334 : bool up;
335 60 : int64 totalrows = WinGetPartitionRowCount(winobj);
336 :
337 : Assert(totalrows > 0);
338 :
339 60 : up = rank_up(winobj);
340 : context = (rank_context *)
341 60 : WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
342 60 : if (up || context->rank == 1)
343 : {
344 : /*
345 : * The current row is not peer to prior row or is just the first, so
346 : * count up the number of rows that are peer to the current.
347 : */
348 : int64 row;
349 :
350 48 : context->rank = WinGetCurrentPosition(winobj) + 1;
351 :
352 : /*
353 : * start from current + 1
354 : */
355 60 : for (row = context->rank; row < totalrows; row++)
356 : {
357 36 : if (!WinRowsArePeers(winobj, row - 1, row))
358 24 : break;
359 12 : context->rank++;
360 : }
361 : }
362 :
363 60 : PG_RETURN_FLOAT8((float8) context->rank / (float8) totalrows);
364 : }
365 :
366 : /*
367 : * window_cume_dist_support
368 : * prosupport function for window_cume_dist()
369 : */
370 : Datum
371 24 : window_cume_dist_support(PG_FUNCTION_ARGS)
372 : {
373 24 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
374 :
375 24 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
376 : {
377 0 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
378 :
379 : /* cume_dist() is monotonically increasing */
380 0 : req->monotonic = MONOTONICFUNC_INCREASING;
381 0 : PG_RETURN_POINTER(req);
382 : }
383 :
384 24 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
385 : {
386 12 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
387 :
388 : /*
389 : * cume_dist() is unaffected by the frame options. Here we set the
390 : * frame options to match what's done in row_number's support
391 : * function. Using ROWS instead of RANGE (the default) saves the
392 : * executor from having to check for peer rows.
393 : */
394 12 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
395 : FRAMEOPTION_ROWS |
396 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
397 : FRAMEOPTION_END_CURRENT_ROW);
398 :
399 12 : PG_RETURN_POINTER(req);
400 : }
401 :
402 12 : PG_RETURN_POINTER(NULL);
403 : }
404 :
405 : /*
406 : * ntile
407 : * compute an exact numeric value with scale 0 (zero),
408 : * ranging from 1 (one) to n, per spec.
409 : */
410 : Datum
411 114 : window_ntile(PG_FUNCTION_ARGS)
412 : {
413 114 : WindowObject winobj = PG_WINDOW_OBJECT();
414 : ntile_context *context;
415 :
416 : context = (ntile_context *)
417 114 : WinGetPartitionLocalMemory(winobj, sizeof(ntile_context));
418 :
419 114 : if (context->ntile == 0)
420 : {
421 : /* first call */
422 : int64 total;
423 : int32 nbuckets;
424 : bool isnull;
425 :
426 42 : total = WinGetPartitionRowCount(winobj);
427 42 : nbuckets = DatumGetInt32(WinGetFuncArgCurrent(winobj, 0, &isnull));
428 :
429 : /*
430 : * per spec: If NT is the null value, then the result is the null
431 : * value.
432 : */
433 42 : if (isnull)
434 12 : PG_RETURN_NULL();
435 :
436 : /*
437 : * per spec: If NT is less than or equal to 0 (zero), then an
438 : * exception condition is raised.
439 : */
440 30 : if (nbuckets <= 0)
441 6 : ereport(ERROR,
442 : (errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTILE),
443 : errmsg("argument of ntile must be greater than zero")));
444 :
445 24 : context->ntile = 1;
446 24 : context->rows_per_bucket = 0;
447 24 : context->boundary = total / nbuckets;
448 24 : if (context->boundary <= 0)
449 0 : context->boundary = 1;
450 : else
451 : {
452 : /*
453 : * If the total number is not divisible, add 1 row to leading
454 : * buckets.
455 : */
456 24 : context->remainder = total % nbuckets;
457 24 : if (context->remainder != 0)
458 18 : context->boundary++;
459 : }
460 : }
461 :
462 96 : context->rows_per_bucket++;
463 96 : if (context->boundary < context->rows_per_bucket)
464 : {
465 : /* ntile up */
466 18 : if (context->remainder != 0 && context->ntile == context->remainder)
467 : {
468 6 : context->remainder = 0;
469 6 : context->boundary -= 1;
470 : }
471 18 : context->ntile += 1;
472 18 : context->rows_per_bucket = 1;
473 : }
474 :
475 96 : PG_RETURN_INT32(context->ntile);
476 : }
477 :
478 : /*
479 : * window_ntile_support
480 : * prosupport function for window_ntile()
481 : */
482 : Datum
483 108 : window_ntile_support(PG_FUNCTION_ARGS)
484 : {
485 108 : Node *rawreq = (Node *) PG_GETARG_POINTER(0);
486 :
487 108 : if (IsA(rawreq, SupportRequestWFuncMonotonic))
488 : {
489 24 : SupportRequestWFuncMonotonic *req = (SupportRequestWFuncMonotonic *) rawreq;
490 :
491 : /*
492 : * ntile() is monotonically increasing as the number of buckets cannot
493 : * change after the first call
494 : */
495 24 : req->monotonic = MONOTONICFUNC_INCREASING;
496 24 : PG_RETURN_POINTER(req);
497 : }
498 :
499 84 : if (IsA(rawreq, SupportRequestOptimizeWindowClause))
500 : {
501 36 : SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
502 :
503 : /*
504 : * ntile() is unaffected by the frame options. Here we set the frame
505 : * options to match what's done in row_number's support function.
506 : * Using ROWS instead of RANGE (the default) saves the executor from
507 : * having to check for peer rows.
508 : */
509 36 : req->frameOptions = (FRAMEOPTION_NONDEFAULT |
510 : FRAMEOPTION_ROWS |
511 : FRAMEOPTION_START_UNBOUNDED_PRECEDING |
512 : FRAMEOPTION_END_CURRENT_ROW);
513 :
514 36 : PG_RETURN_POINTER(req);
515 : }
516 :
517 48 : PG_RETURN_POINTER(NULL);
518 : }
519 :
520 : /*
521 : * leadlag_common
522 : * common operation of lead() and lag()
523 : * For lead() forward is true, whereas for lag() it is false.
524 : * withoffset indicates we have an offset second argument.
525 : * withdefault indicates we have a default third argument.
526 : */
527 : static Datum
528 182778 : leadlag_common(FunctionCallInfo fcinfo,
529 : bool forward, bool withoffset, bool withdefault)
530 : {
531 182778 : WindowObject winobj = PG_WINDOW_OBJECT();
532 : int32 offset;
533 : bool const_offset;
534 : Datum result;
535 : bool isnull;
536 : bool isout;
537 :
538 182778 : if (withoffset)
539 : {
540 540 : offset = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
541 540 : if (isnull)
542 0 : PG_RETURN_NULL();
543 540 : const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);
544 : }
545 : else
546 : {
547 182238 : offset = 1;
548 182238 : const_offset = true;
549 : }
550 :
551 182778 : result = WinGetFuncArgInPartition(winobj, 0,
552 : (forward ? offset : -offset),
553 : WINDOW_SEEK_CURRENT,
554 : const_offset,
555 : &isnull, &isout);
556 :
557 182778 : if (isout)
558 : {
559 : /*
560 : * target row is out of the partition; supply default value if
561 : * provided. otherwise it'll stay NULL
562 : */
563 318 : if (withdefault)
564 96 : result = WinGetFuncArgCurrent(winobj, 2, &isnull);
565 : }
566 :
567 182778 : if (isnull)
568 222 : PG_RETURN_NULL();
569 :
570 182556 : PG_RETURN_DATUM(result);
571 : }
572 :
573 : /*
574 : * lag
575 : * returns the value of VE evaluated on a row that is 1
576 : * row before the current row within a partition,
577 : * per spec.
578 : */
579 : Datum
580 181938 : window_lag(PG_FUNCTION_ARGS)
581 : {
582 181938 : return leadlag_common(fcinfo, false, false, false);
583 : }
584 :
585 : /*
586 : * lag_with_offset
587 : * returns the value of VE evaluated on a row that is OFFSET
588 : * rows before the current row within a partition,
589 : * per spec.
590 : */
591 : Datum
592 120 : window_lag_with_offset(PG_FUNCTION_ARGS)
593 : {
594 120 : return leadlag_common(fcinfo, false, true, false);
595 : }
596 :
597 : /*
598 : * lag_with_offset_and_default
599 : * same as lag_with_offset but accepts default value
600 : * as its third argument.
601 : */
602 : Datum
603 120 : window_lag_with_offset_and_default(PG_FUNCTION_ARGS)
604 : {
605 120 : return leadlag_common(fcinfo, false, true, true);
606 : }
607 :
608 : /*
609 : * lead
610 : * returns the value of VE evaluated on a row that is 1
611 : * row after the current row within a partition,
612 : * per spec.
613 : */
614 : Datum
615 300 : window_lead(PG_FUNCTION_ARGS)
616 : {
617 300 : return leadlag_common(fcinfo, true, false, false);
618 : }
619 :
620 : /*
621 : * lead_with_offset
622 : * returns the value of VE evaluated on a row that is OFFSET
623 : * number of rows after the current row within a partition,
624 : * per spec.
625 : */
626 : Datum
627 180 : window_lead_with_offset(PG_FUNCTION_ARGS)
628 : {
629 180 : return leadlag_common(fcinfo, true, true, false);
630 : }
631 :
632 : /*
633 : * lead_with_offset_and_default
634 : * same as lead_with_offset but accepts default value
635 : * as its third argument.
636 : */
637 : Datum
638 120 : window_lead_with_offset_and_default(PG_FUNCTION_ARGS)
639 : {
640 120 : return leadlag_common(fcinfo, true, true, true);
641 : }
642 :
643 : /*
644 : * first_value
645 : * return the value of VE evaluated on the first row of the
646 : * window frame, per spec.
647 : */
648 : Datum
649 3726 : window_first_value(PG_FUNCTION_ARGS)
650 : {
651 3726 : WindowObject winobj = PG_WINDOW_OBJECT();
652 : Datum result;
653 : bool isnull;
654 :
655 3726 : result = WinGetFuncArgInFrame(winobj, 0,
656 : 0, WINDOW_SEEK_HEAD, true,
657 : &isnull, NULL);
658 3654 : if (isnull)
659 354 : PG_RETURN_NULL();
660 :
661 3300 : PG_RETURN_DATUM(result);
662 : }
663 :
664 : /*
665 : * last_value
666 : * return the value of VE evaluated on the last row of the
667 : * window frame, per spec.
668 : */
669 : Datum
670 4422 : window_last_value(PG_FUNCTION_ARGS)
671 : {
672 4422 : WindowObject winobj = PG_WINDOW_OBJECT();
673 : Datum result;
674 : bool isnull;
675 :
676 4422 : result = WinGetFuncArgInFrame(winobj, 0,
677 : 0, WINDOW_SEEK_TAIL, true,
678 : &isnull, NULL);
679 4416 : if (isnull)
680 348 : PG_RETURN_NULL();
681 :
682 4068 : PG_RETURN_DATUM(result);
683 : }
684 :
685 : /*
686 : * nth_value
687 : * return the value of VE evaluated on the n-th row from the first
688 : * row of the window frame, per spec.
689 : */
690 : Datum
691 486 : window_nth_value(PG_FUNCTION_ARGS)
692 : {
693 486 : WindowObject winobj = PG_WINDOW_OBJECT();
694 : bool const_offset;
695 : Datum result;
696 : bool isnull;
697 : int32 nth;
698 :
699 486 : nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
700 486 : if (isnull)
701 0 : PG_RETURN_NULL();
702 486 : const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);
703 :
704 486 : if (nth <= 0)
705 6 : ereport(ERROR,
706 : (errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTH_VALUE),
707 : errmsg("argument of nth_value must be greater than zero")));
708 :
709 480 : result = WinGetFuncArgInFrame(winobj, 0,
710 : nth - 1, WINDOW_SEEK_HEAD, const_offset,
711 : &isnull, NULL);
712 480 : if (isnull)
713 54 : PG_RETURN_NULL();
714 :
715 426 : PG_RETURN_DATUM(result);
716 : }
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