1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>43.6. Control Structures</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plpgsql-statements.html" title="43.5. Basic Statements" /><link rel="next" href="plpgsql-cursors.html" title="43.7. Cursors" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">43.6. Control Structures</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql-statements.html" title="43.5. Basic Statements">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 43. PL/pgSQL — SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 43. <span class="application">PL/pgSQL</span> — <acronym class="acronym">SQL</acronym> Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpgsql-cursors.html" title="43.7. Cursors">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLPGSQL-CONTROL-STRUCTURES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">43.6. Control Structures <a href="#PLPGSQL-CONTROL-STRUCTURES" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING">43.6.1. Returning from a Function</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING-PROCEDURE">43.6.2. Returning from a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-CALLING-PROCEDURE">43.6.3. Calling a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONDITIONALS">43.6.4. Conditionals</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONTROL-STRUCTURES-LOOPS">43.6.5. Simple Loops</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING">43.6.6. Looping through Query Results</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-FOREACH-ARRAY">43.6.7. Looping through Arrays</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING">43.6.8. Trapping Errors</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK">43.6.9. Obtaining Execution Location Information</a></span></dt></dl></div><p>
Control structures are probably the most useful (and
important) part of <span class="application">PL/pgSQL</span>. With
<span class="application">PL/pgSQL</span>'s control structures,
you can manipulate <span class="productname">PostgreSQL</span> data in a very
flexible and powerful way.
</p><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING"><div class="titlepage"><div><div><h3 class="title">43.6.1. Returning from a Function <a href="#PLPGSQL-STATEMENTS-RETURNING" class="id_link">#</a></h3></div></div></div><p>
There are two commands available that allow you to return data
from a function: <code class="command">RETURN</code> and <code class="command">RETURN
NEXT</code>.
</p><div class="sect3" id="PLPGSQL-STATEMENTS-RETURNING-RETURN"><div class="titlepage"><div><div><h4 class="title">43.6.1.1. <code class="command">RETURN</code> <a href="#PLPGSQL-STATEMENTS-RETURNING-RETURN" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
RETURN <em class="replaceable"><code>expression</code></em>;
</pre><p>
<code class="command">RETURN</code> with an expression terminates the
function and returns the value of
<em class="replaceable"><code>expression</code></em> to the caller. This form
is used for <span class="application">PL/pgSQL</span> functions that do
not return a set.
</p><p>
In a function that returns a scalar type, the expression's result will
automatically be cast into the function's return type as described for
assignments. But to return a composite (row) value, you must write an
expression delivering exactly the requested column set. This may
require use of explicit casting.
</p><p>
If you declared the function with output parameters, write just
<code class="command">RETURN</code> with no expression. The current values
of the output parameter variables will be returned.
</p><p>
If you declared the function to return <code class="type">void</code>, a
<code class="command">RETURN</code> statement can be used to exit the function
early; but do not write an expression following
<code class="command">RETURN</code>.
</p><p>
The return value of a function cannot be left undefined. If
control reaches the end of the top-level block of the function
without hitting a <code class="command">RETURN</code> statement, a run-time
error will occur. This restriction does not apply to functions
with output parameters and functions returning <code class="type">void</code>,
however. In those cases a <code class="command">RETURN</code> statement is
automatically executed if the top-level block finishes.
</p><p>
Some examples:
</p><pre class="programlisting">
-- functions returning a scalar type
RETURN 1 + 2;
RETURN scalar_var;
-- functions returning a composite type
RETURN composite_type_var;
RETURN (1, 2, 'three'::text); -- must cast columns to correct types
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-STATEMENTS-RETURNING-RETURN-NEXT"><div class="titlepage"><div><div><h4 class="title">43.6.1.2. <code class="command">RETURN NEXT</code> and <code class="command">RETURN QUERY</code> <a href="#PLPGSQL-STATEMENTS-RETURNING-RETURN-NEXT" class="id_link">#</a></h4></div></div></div><a id="id-1.8.8.8.3.4.2" class="indexterm"></a><a id="id-1.8.8.8.3.4.3" class="indexterm"></a><pre class="synopsis">
RETURN NEXT <em class="replaceable"><code>expression</code></em>;
RETURN QUERY <em class="replaceable"><code>query</code></em>;
RETURN QUERY EXECUTE <em class="replaceable"><code>command-string</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>];
</pre><p>
When a <span class="application">PL/pgSQL</span> function is declared to return
<code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code>, the procedure
to follow is slightly different. In that case, the individual
items to return are specified by a sequence of <code class="command">RETURN
NEXT</code> or <code class="command">RETURN QUERY</code> commands, and
then a final <code class="command">RETURN</code> command with no argument
is used to indicate that the function has finished executing.
<code class="command">RETURN NEXT</code> can be used with both scalar and
composite data types; with a composite result type, an entire
<span class="quote">“<span class="quote">table</span>”</span> of results will be returned.
<code class="command">RETURN QUERY</code> appends the results of executing
a query to the function's result set. <code class="command">RETURN
NEXT</code> and <code class="command">RETURN QUERY</code> can be freely
intermixed in a single set-returning function, in which case
their results will be concatenated.
</p><p>
<code class="command">RETURN NEXT</code> and <code class="command">RETURN
QUERY</code> do not actually return from the function —
they simply append zero or more rows to the function's result
set. Execution then continues with the next statement in the
<span class="application">PL/pgSQL</span> function. As successive
<code class="command">RETURN NEXT</code> or <code class="command">RETURN
QUERY</code> commands are executed, the result set is built
up. A final <code class="command">RETURN</code>, which should have no
argument, causes control to exit the function (or you can just
let control reach the end of the function).
</p><p>
<code class="command">RETURN QUERY</code> has a variant
<code class="command">RETURN QUERY EXECUTE</code>, which specifies the
query to be executed dynamically. Parameter expressions can
be inserted into the computed query string via <code class="literal">USING</code>,
in just the same way as in the <code class="command">EXECUTE</code> command.
</p><p>
If you declared the function with output parameters, write just
<code class="command">RETURN NEXT</code> with no expression. On each
execution, the current values of the output parameter
variable(s) will be saved for eventual return as a row of the
result. Note that you must declare the function as returning
<code class="literal">SETOF record</code> when there are multiple output
parameters, or <code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code>
when there is just one output parameter of type
<em class="replaceable"><code>sometype</code></em>, in order to create a set-returning
function with output parameters.
</p><p>
Here is an example of a function using <code class="command">RETURN
NEXT</code>:
</p><pre class="programlisting">
CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT);
INSERT INTO foo VALUES (1, 2, 'three');
INSERT INTO foo VALUES (4, 5, 'six');
CREATE OR REPLACE FUNCTION get_all_foo() RETURNS SETOF foo AS
$BODY$
DECLARE
r foo%rowtype;
BEGIN
FOR r IN
SELECT * FROM foo WHERE fooid > 0
LOOP
-- can do some processing here
RETURN NEXT r; -- return current row of SELECT
END LOOP;
RETURN;
END;
$BODY$
LANGUAGE plpgsql;
SELECT * FROM get_all_foo();
</pre><p>
</p><p>
Here is an example of a function using <code class="command">RETURN
QUERY</code>:
</p><pre class="programlisting">
CREATE FUNCTION get_available_flightid(date) RETURNS SETOF integer AS
$BODY$
BEGIN
RETURN QUERY SELECT flightid
FROM flight
WHERE flightdate >= $1
AND flightdate < ($1 + 1);
-- Since execution is not finished, we can check whether rows were returned
-- and raise exception if not.
IF NOT FOUND THEN
RAISE EXCEPTION 'No flight at %.', $1;
END IF;
RETURN;
END;
$BODY$
LANGUAGE plpgsql;
-- Returns available flights or raises exception if there are no
-- available flights.
SELECT * FROM get_available_flightid(CURRENT_DATE);
</pre><p>
</p><div class="note"><h3 class="title">Note</h3><p>
The current implementation of <code class="command">RETURN NEXT</code>
and <code class="command">RETURN QUERY</code> stores the entire result set
before returning from the function, as discussed above. That
means that if a <span class="application">PL/pgSQL</span> function produces a
very large result set, performance might be poor: data will be
written to disk to avoid memory exhaustion, but the function
itself will not return until the entire result set has been
generated. A future version of <span class="application">PL/pgSQL</span> might
allow users to define set-returning functions
that do not have this limitation. Currently, the point at
which data begins being written to disk is controlled by the
<a class="xref" href="runtime-config-resource.html#GUC-WORK-MEM">work_mem</a>
configuration variable. Administrators who have sufficient
memory to store larger result sets in memory should consider
increasing this parameter.
</p></div></div></div><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">43.6.2. Returning from a Procedure <a href="#PLPGSQL-STATEMENTS-RETURNING-PROCEDURE" class="id_link">#</a></h3></div></div></div><p>
A procedure does not have a return value. A procedure can therefore end
without a <code class="command">RETURN</code> statement. If you wish to use
a <code class="command">RETURN</code> statement to exit the code early, write
just <code class="command">RETURN</code> with no expression.
</p><p>
If the procedure has output parameters, the final values of the output
parameter variables will be returned to the caller.
</p></div><div class="sect2" id="PLPGSQL-STATEMENTS-CALLING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">43.6.3. Calling a Procedure <a href="#PLPGSQL-STATEMENTS-CALLING-PROCEDURE" class="id_link">#</a></h3></div></div></div><p>
A <span class="application">PL/pgSQL</span> function, procedure,
or <code class="command">DO</code> block can call a procedure
using <code class="command">CALL</code>. Output parameters are handled
differently from the way that <code class="command">CALL</code> works in plain
SQL. Each <code class="literal">OUT</code> or <code class="literal">INOUT</code>
parameter of the procedure must
correspond to a variable in the <code class="command">CALL</code> statement, and
whatever the procedure returns is assigned back to that variable after
it returns. For example:
</p><pre class="programlisting">
CREATE PROCEDURE triple(INOUT x int)
LANGUAGE plpgsql
AS $$
BEGIN
x := x * 3;
END;
$$;
DO $$
DECLARE myvar int := 5;
BEGIN
CALL triple(myvar);
RAISE NOTICE 'myvar = %', myvar; -- prints 15
END;
$$;
</pre><p>
The variable corresponding to an output parameter can be a simple
variable or a field of a composite-type variable. Currently,
it cannot be an element of an array.
</p></div><div class="sect2" id="PLPGSQL-CONDITIONALS"><div class="titlepage"><div><div><h3 class="title">43.6.4. Conditionals <a href="#PLPGSQL-CONDITIONALS" class="id_link">#</a></h3></div></div></div><p>
<code class="command">IF</code> and <code class="command">CASE</code> statements let you execute
alternative commands based on certain conditions.
<span class="application">PL/pgSQL</span> has three forms of <code class="command">IF</code>:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">IF ... THEN ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSE ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF</code></p></li></ul></div><p>
and two forms of <code class="command">CASE</code>:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">CASE ... WHEN ... THEN ... ELSE ... END CASE</code></p></li><li class="listitem"><p><code class="literal">CASE WHEN ... THEN ... ELSE ... END CASE</code></p></li></ul></div><p>
</p><div class="sect3" id="PLPGSQL-CONDITIONALS-IF-THEN"><div class="titlepage"><div><div><h4 class="title">43.6.4.1. <code class="literal">IF-THEN</code> <a href="#PLPGSQL-CONDITIONALS-IF-THEN" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
IF <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
END IF;
</pre><p>
<code class="literal">IF-THEN</code> statements are the simplest form of
<code class="literal">IF</code>. The statements between
<code class="literal">THEN</code> and <code class="literal">END IF</code> will be
executed if the condition is true. Otherwise, they are
skipped.
</p><p>
Example:
</p><pre class="programlisting">
IF v_user_id <> 0 THEN
UPDATE users SET email = v_email WHERE user_id = v_user_id;
END IF;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-CONDITIONALS-IF-THEN-ELSE"><div class="titlepage"><div><div><h4 class="title">43.6.4.2. <code class="literal">IF-THEN-ELSE</code> <a href="#PLPGSQL-CONDITIONALS-IF-THEN-ELSE" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
IF <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
ELSE
<em class="replaceable"><code>statements</code></em>
END IF;
</pre><p>
<code class="literal">IF-THEN-ELSE</code> statements add to
<code class="literal">IF-THEN</code> by letting you specify an
alternative set of statements that should be executed if the
condition is not true. (Note this includes the case where the
condition evaluates to NULL.)
</p><p>
Examples:
</p><pre class="programlisting">
IF parentid IS NULL OR parentid = ''
THEN
RETURN fullname;
ELSE
RETURN hp_true_filename(parentid) || '/' || fullname;
END IF;
</pre><p>
</p><pre class="programlisting">
IF v_count > 0 THEN
INSERT INTO users_count (count) VALUES (v_count);
RETURN 't';
ELSE
RETURN 'f';
END IF;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-CONDITIONALS-IF-THEN-ELSIF"><div class="titlepage"><div><div><h4 class="title">43.6.4.3. <code class="literal">IF-THEN-ELSIF</code> <a href="#PLPGSQL-CONDITIONALS-IF-THEN-ELSIF" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
IF <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
[<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
[<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
...
</span>]
</span>]
[<span class="optional"> ELSE
<em class="replaceable"><code>statements</code></em> </span>]
END IF;
</pre><p>
Sometimes there are more than just two alternatives.
<code class="literal">IF-THEN-ELSIF</code> provides a convenient
method of checking several alternatives in turn.
The <code class="literal">IF</code> conditions are tested successively
until the first one that is true is found. Then the
associated statement(s) are executed, after which control
passes to the next statement after <code class="literal">END IF</code>.
(Any subsequent <code class="literal">IF</code> conditions are <span class="emphasis"><em>not</em></span>
tested.) If none of the <code class="literal">IF</code> conditions is true,
then the <code class="literal">ELSE</code> block (if any) is executed.
</p><p>
Here is an example:
</p><pre class="programlisting">
IF number = 0 THEN
result := 'zero';
ELSIF number > 0 THEN
result := 'positive';
ELSIF number < 0 THEN
result := 'negative';
ELSE
-- hmm, the only other possibility is that number is null
result := 'NULL';
END IF;
</pre><p>
</p><p>
The key word <code class="literal">ELSIF</code> can also be spelled
<code class="literal">ELSEIF</code>.
</p><p>
An alternative way of accomplishing the same task is to nest
<code class="literal">IF-THEN-ELSE</code> statements, as in the
following example:
</p><pre class="programlisting">
IF demo_row.sex = 'm' THEN
pretty_sex := 'man';
ELSE
IF demo_row.sex = 'f' THEN
pretty_sex := 'woman';
END IF;
END IF;
</pre><p>
</p><p>
However, this method requires writing a matching <code class="literal">END IF</code>
for each <code class="literal">IF</code>, so it is much more cumbersome than
using <code class="literal">ELSIF</code> when there are many alternatives.
</p></div><div class="sect3" id="PLPGSQL-CONDITIONALS-SIMPLE-CASE"><div class="titlepage"><div><div><h4 class="title">43.6.4.4. Simple <code class="literal">CASE</code> <a href="#PLPGSQL-CONDITIONALS-SIMPLE-CASE" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
CASE <em class="replaceable"><code>search-expression</code></em>
WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN
<em class="replaceable"><code>statements</code></em>
[<span class="optional"> WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN
<em class="replaceable"><code>statements</code></em>
... </span>]
[<span class="optional"> ELSE
<em class="replaceable"><code>statements</code></em> </span>]
END CASE;
</pre><p>
The simple form of <code class="command">CASE</code> provides conditional execution
based on equality of operands. The <em class="replaceable"><code>search-expression</code></em>
is evaluated (once) and successively compared to each
<em class="replaceable"><code>expression</code></em> in the <code class="literal">WHEN</code> clauses.
If a match is found, then the corresponding
<em class="replaceable"><code>statements</code></em> are executed, and then control
passes to the next statement after <code class="literal">END CASE</code>. (Subsequent
<code class="literal">WHEN</code> expressions are not evaluated.) If no match is
found, the <code class="literal">ELSE</code> <em class="replaceable"><code>statements</code></em> are
executed; but if <code class="literal">ELSE</code> is not present, then a
<code class="literal">CASE_NOT_FOUND</code> exception is raised.
</p><p>
Here is a simple example:
</p><pre class="programlisting">
CASE x
WHEN 1, 2 THEN
msg := 'one or two';
ELSE
msg := 'other value than one or two';
END CASE;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-CONDITIONALS-SEARCHED-CASE"><div class="titlepage"><div><div><h4 class="title">43.6.4.5. Searched <code class="literal">CASE</code> <a href="#PLPGSQL-CONDITIONALS-SEARCHED-CASE" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
CASE
WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
[<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN
<em class="replaceable"><code>statements</code></em>
... </span>]
[<span class="optional"> ELSE
<em class="replaceable"><code>statements</code></em> </span>]
END CASE;
</pre><p>
The searched form of <code class="command">CASE</code> provides conditional execution
based on truth of Boolean expressions. Each <code class="literal">WHEN</code> clause's
<em class="replaceable"><code>boolean-expression</code></em> is evaluated in turn,
until one is found that yields <code class="literal">true</code>. Then the
corresponding <em class="replaceable"><code>statements</code></em> are executed, and
then control passes to the next statement after <code class="literal">END CASE</code>.
(Subsequent <code class="literal">WHEN</code> expressions are not evaluated.)
If no true result is found, the <code class="literal">ELSE</code>
<em class="replaceable"><code>statements</code></em> are executed;
but if <code class="literal">ELSE</code> is not present, then a
<code class="literal">CASE_NOT_FOUND</code> exception is raised.
</p><p>
Here is an example:
</p><pre class="programlisting">
CASE
WHEN x BETWEEN 0 AND 10 THEN
msg := 'value is between zero and ten';
WHEN x BETWEEN 11 AND 20 THEN
msg := 'value is between eleven and twenty';
END CASE;
</pre><p>
</p><p>
This form of <code class="command">CASE</code> is entirely equivalent to
<code class="literal">IF-THEN-ELSIF</code>, except for the rule that reaching
an omitted <code class="literal">ELSE</code> clause results in an error rather
than doing nothing.
</p></div></div><div class="sect2" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS"><div class="titlepage"><div><div><h3 class="title">43.6.5. Simple Loops <a href="#PLPGSQL-CONTROL-STRUCTURES-LOOPS" class="id_link">#</a></h3></div></div></div><a id="id-1.8.8.8.7.2" class="indexterm"></a><p>
With the <code class="literal">LOOP</code>, <code class="literal">EXIT</code>,
<code class="literal">CONTINUE</code>, <code class="literal">WHILE</code>, <code class="literal">FOR</code>,
and <code class="literal">FOREACH</code> statements, you can arrange for your
<span class="application">PL/pgSQL</span> function to repeat a series of commands.
</p><div class="sect3" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS-LOOP"><div class="titlepage"><div><div><h4 class="title">43.6.5.1. <code class="literal">LOOP</code> <a href="#PLPGSQL-CONTROL-STRUCTURES-LOOPS-LOOP" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
<code class="literal">LOOP</code> defines an unconditional loop that is repeated
indefinitely until terminated by an <code class="literal">EXIT</code> or
<code class="command">RETURN</code> statement. The optional
<em class="replaceable"><code>label</code></em> can be used by <code class="literal">EXIT</code>
and <code class="literal">CONTINUE</code> statements within nested loops to
specify which loop those statements refer to.
</p></div><div class="sect3" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS-EXIT"><div class="titlepage"><div><div><h4 class="title">43.6.5.2. <code class="literal">EXIT</code> <a href="#PLPGSQL-CONTROL-STRUCTURES-LOOPS-EXIT" class="id_link">#</a></h4></div></div></div><a id="id-1.8.8.8.7.5.2" class="indexterm"></a><pre class="synopsis">
EXIT [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>];
</pre><p>
If no <em class="replaceable"><code>label</code></em> is given, the innermost
loop is terminated and the statement following <code class="literal">END
LOOP</code> is executed next. If <em class="replaceable"><code>label</code></em>
is given, it must be the label of the current or some outer
level of nested loop or block. Then the named loop or block is
terminated and control continues with the statement after the
loop's/block's corresponding <code class="literal">END</code>.
</p><p>
If <code class="literal">WHEN</code> is specified, the loop exit occurs only if
<em class="replaceable"><code>boolean-expression</code></em> is true. Otherwise, control passes
to the statement after <code class="literal">EXIT</code>.
</p><p>
<code class="literal">EXIT</code> can be used with all types of loops; it is
not limited to use with unconditional loops.
</p><p>
When used with a
<code class="literal">BEGIN</code> block, <code class="literal">EXIT</code> passes
control to the next statement after the end of the block.
Note that a label must be used for this purpose; an unlabeled
<code class="literal">EXIT</code> is never considered to match a
<code class="literal">BEGIN</code> block. (This is a change from
pre-8.4 releases of <span class="productname">PostgreSQL</span>, which
would allow an unlabeled <code class="literal">EXIT</code> to match
a <code class="literal">BEGIN</code> block.)
</p><p>
Examples:
</p><pre class="programlisting">
LOOP
-- some computations
IF count > 0 THEN
EXIT; -- exit loop
END IF;
END LOOP;
LOOP
-- some computations
EXIT WHEN count > 0; -- same result as previous example
END LOOP;
<<ablock>>
BEGIN
-- some computations
IF stocks > 100000 THEN
EXIT ablock; -- causes exit from the BEGIN block
END IF;
-- computations here will be skipped when stocks > 100000
END;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS-CONTINUE"><div class="titlepage"><div><div><h4 class="title">43.6.5.3. <code class="literal">CONTINUE</code> <a href="#PLPGSQL-CONTROL-STRUCTURES-LOOPS-CONTINUE" class="id_link">#</a></h4></div></div></div><a id="id-1.8.8.8.7.6.2" class="indexterm"></a><pre class="synopsis">
CONTINUE [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>];
</pre><p>
If no <em class="replaceable"><code>label</code></em> is given, the next iteration of
the innermost loop is begun. That is, all statements remaining
in the loop body are skipped, and control returns
to the loop control expression (if any) to determine whether
another loop iteration is needed.
If <em class="replaceable"><code>label</code></em> is present, it
specifies the label of the loop whose execution will be
continued.
</p><p>
If <code class="literal">WHEN</code> is specified, the next iteration of the
loop is begun only if <em class="replaceable"><code>boolean-expression</code></em> is
true. Otherwise, control passes to the statement after
<code class="literal">CONTINUE</code>.
</p><p>
<code class="literal">CONTINUE</code> can be used with all types of loops; it
is not limited to use with unconditional loops.
</p><p>
Examples:
</p><pre class="programlisting">
LOOP
-- some computations
EXIT WHEN count > 100;
CONTINUE WHEN count < 50;
-- some computations for count IN [50 .. 100]
END LOOP;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS-WHILE"><div class="titlepage"><div><div><h4 class="title">43.6.5.4. <code class="literal">WHILE</code> <a href="#PLPGSQL-CONTROL-STRUCTURES-LOOPS-WHILE" class="id_link">#</a></h4></div></div></div><a id="id-1.8.8.8.7.7.2" class="indexterm"></a><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
WHILE <em class="replaceable"><code>boolean-expression</code></em> LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
The <code class="literal">WHILE</code> statement repeats a
sequence of statements so long as the
<em class="replaceable"><code>boolean-expression</code></em>
evaluates to true. The expression is checked just before
each entry to the loop body.
</p><p>
For example:
</p><pre class="programlisting">
WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP
-- some computations here
END LOOP;
WHILE NOT done LOOP
-- some computations here
END LOOP;
</pre><p>
</p></div><div class="sect3" id="PLPGSQL-INTEGER-FOR"><div class="titlepage"><div><div><h4 class="title">43.6.5.5. <code class="literal">FOR</code> (Integer Variant) <a href="#PLPGSQL-INTEGER-FOR" class="id_link">#</a></h4></div></div></div><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
FOR <em class="replaceable"><code>name</code></em> IN [<span class="optional"> REVERSE </span>] <em class="replaceable"><code>expression</code></em> .. <em class="replaceable"><code>expression</code></em> [<span class="optional"> BY <em class="replaceable"><code>expression</code></em> </span>] LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
This form of <code class="literal">FOR</code> creates a loop that iterates over a range
of integer values. The variable
<em class="replaceable"><code>name</code></em> is automatically defined as type
<code class="type">integer</code> and exists only inside the loop (any existing
definition of the variable name is ignored within the loop).
The two expressions giving
the lower and upper bound of the range are evaluated once when entering
the loop. If the <code class="literal">BY</code> clause isn't specified the iteration
step is 1, otherwise it's the value specified in the <code class="literal">BY</code>
clause, which again is evaluated once on loop entry.
If <code class="literal">REVERSE</code> is specified then the step value is
subtracted, rather than added, after each iteration.
</p><p>
Some examples of integer <code class="literal">FOR</code> loops:
</p><pre class="programlisting">
FOR i IN 1..10 LOOP
-- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop
END LOOP;
FOR i IN REVERSE 10..1 LOOP
-- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop
END LOOP;
FOR i IN REVERSE 10..1 BY 2 LOOP
-- i will take on the values 10,8,6,4,2 within the loop
END LOOP;
</pre><p>
</p><p>
If the lower bound is greater than the upper bound (or less than,
in the <code class="literal">REVERSE</code> case), the loop body is not
executed at all. No error is raised.
</p><p>
If a <em class="replaceable"><code>label</code></em> is attached to the
<code class="literal">FOR</code> loop then the integer loop variable can be
referenced with a qualified name, using that
<em class="replaceable"><code>label</code></em>.
</p></div></div><div class="sect2" id="PLPGSQL-RECORDS-ITERATING"><div class="titlepage"><div><div><h3 class="title">43.6.6. Looping through Query Results <a href="#PLPGSQL-RECORDS-ITERATING" class="id_link">#</a></h3></div></div></div><p>
Using a different type of <code class="literal">FOR</code> loop, you can iterate through
the results of a query and manipulate that data
accordingly. The syntax is:
</p><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
FOR <em class="replaceable"><code>target</code></em> IN <em class="replaceable"><code>query</code></em> LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
The <em class="replaceable"><code>target</code></em> is a record variable, row variable,
or comma-separated list of scalar variables.
The <em class="replaceable"><code>target</code></em> is successively assigned each row
resulting from the <em class="replaceable"><code>query</code></em> and the loop body is
executed for each row. Here is an example:
</p><pre class="programlisting">
CREATE FUNCTION refresh_mviews() RETURNS integer AS $$
DECLARE
mviews RECORD;
BEGIN
RAISE NOTICE 'Refreshing all materialized views...';
FOR mviews IN
SELECT n.nspname AS mv_schema,
c.relname AS mv_name,
pg_catalog.pg_get_userbyid(c.relowner) AS owner
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_namespace n ON (n.oid = c.relnamespace)
WHERE c.relkind = 'm'
ORDER BY 1
LOOP
-- Now "mviews" has one record with information about the materialized view
RAISE NOTICE 'Refreshing materialized view %.% (owner: %)...',
quote_ident(mviews.mv_schema),
quote_ident(mviews.mv_name),
quote_ident(mviews.owner);
EXECUTE format('REFRESH MATERIALIZED VIEW %I.%I', mviews.mv_schema, mviews.mv_name);
END LOOP;
RAISE NOTICE 'Done refreshing materialized views.';
RETURN 1;
END;
$$ LANGUAGE plpgsql;
</pre><p>
If the loop is terminated by an <code class="literal">EXIT</code> statement, the last
assigned row value is still accessible after the loop.
</p><p>
The <em class="replaceable"><code>query</code></em> used in this type of <code class="literal">FOR</code>
statement can be any SQL command that returns rows to the caller:
<code class="command">SELECT</code> is the most common case,
but you can also use <code class="command">INSERT</code>, <code class="command">UPDATE</code>, or
<code class="command">DELETE</code> with a <code class="literal">RETURNING</code> clause. Some utility
commands such as <code class="command">EXPLAIN</code> will work too.
</p><p>
<span class="application">PL/pgSQL</span> variables are replaced by query parameters,
and the query plan is cached for possible re-use, as discussed in
detail in <a class="xref" href="plpgsql-implementation.html#PLPGSQL-VAR-SUBST" title="43.11.1. Variable Substitution">Section 43.11.1</a> and
<a class="xref" href="plpgsql-implementation.html#PLPGSQL-PLAN-CACHING" title="43.11.2. Plan Caching">Section 43.11.2</a>.
</p><p>
The <code class="literal">FOR-IN-EXECUTE</code> statement is another way to iterate over
rows:
</p><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
FOR <em class="replaceable"><code>target</code></em> IN EXECUTE <em class="replaceable"><code>text_expression</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>] LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
This is like the previous form, except that the source query
is specified as a string expression, which is evaluated and replanned
on each entry to the <code class="literal">FOR</code> loop. This allows the programmer to
choose the speed of a preplanned query or the flexibility of a dynamic
query, just as with a plain <code class="command">EXECUTE</code> statement.
As with <code class="command">EXECUTE</code>, parameter values can be inserted
into the dynamic command via <code class="literal">USING</code>.
</p><p>
Another way to specify the query whose results should be iterated
through is to declare it as a cursor. This is described in
<a class="xref" href="plpgsql-cursors.html#PLPGSQL-CURSOR-FOR-LOOP" title="43.7.4. Looping through a Cursor's Result">Section 43.7.4</a>.
</p></div><div class="sect2" id="PLPGSQL-FOREACH-ARRAY"><div class="titlepage"><div><div><h3 class="title">43.6.7. Looping through Arrays <a href="#PLPGSQL-FOREACH-ARRAY" class="id_link">#</a></h3></div></div></div><p>
The <code class="literal">FOREACH</code> loop is much like a <code class="literal">FOR</code> loop,
but instead of iterating through the rows returned by an SQL query,
it iterates through the elements of an array value.
(In general, <code class="literal">FOREACH</code> is meant for looping through
components of a composite-valued expression; variants for looping
through composites besides arrays may be added in future.)
The <code class="literal">FOREACH</code> statement to loop over an array is:
</p><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
FOREACH <em class="replaceable"><code>target</code></em> [<span class="optional"> SLICE <em class="replaceable"><code>number</code></em> </span>] IN ARRAY <em class="replaceable"><code>expression</code></em> LOOP
<em class="replaceable"><code>statements</code></em>
END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
</p><p>
Without <code class="literal">SLICE</code>, or if <code class="literal">SLICE 0</code> is specified,
the loop iterates through individual elements of the array produced
by evaluating the <em class="replaceable"><code>expression</code></em>.
The <em class="replaceable"><code>target</code></em> variable is assigned each
element value in sequence, and the loop body is executed for each element.
Here is an example of looping through the elements of an integer
array:
</p><pre class="programlisting">
CREATE FUNCTION sum(int[]) RETURNS int8 AS $$
DECLARE
s int8 := 0;
x int;
BEGIN
FOREACH x IN ARRAY $1
LOOP
s := s + x;
END LOOP;
RETURN s;
END;
$$ LANGUAGE plpgsql;
</pre><p>
The elements are visited in storage order, regardless of the number of
array dimensions. Although the <em class="replaceable"><code>target</code></em> is
usually just a single variable, it can be a list of variables when
looping through an array of composite values (records). In that case,
for each array element, the variables are assigned from successive
columns of the composite value.
</p><p>
With a positive <code class="literal">SLICE</code> value, <code class="literal">FOREACH</code>
iterates through slices of the array rather than single elements.
The <code class="literal">SLICE</code> value must be an integer constant not larger
than the number of dimensions of the array. The
<em class="replaceable"><code>target</code></em> variable must be an array,
and it receives successive slices of the array value, where each slice
is of the number of dimensions specified by <code class="literal">SLICE</code>.
Here is an example of iterating through one-dimensional slices:
</p><pre class="programlisting">
CREATE FUNCTION scan_rows(int[]) RETURNS void AS $$
DECLARE
x int[];
BEGIN
FOREACH x SLICE 1 IN ARRAY $1
LOOP
RAISE NOTICE 'row = %', x;
END LOOP;
END;
$$ LANGUAGE plpgsql;
SELECT scan_rows(ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);
NOTICE: row = {1,2,3}
NOTICE: row = {4,5,6}
NOTICE: row = {7,8,9}
NOTICE: row = {10,11,12}
</pre><p>
</p></div><div class="sect2" id="PLPGSQL-ERROR-TRAPPING"><div class="titlepage"><div><div><h3 class="title">43.6.8. Trapping Errors <a href="#PLPGSQL-ERROR-TRAPPING" class="id_link">#</a></h3></div></div></div><a id="id-1.8.8.8.10.2" class="indexterm"></a><p>
By default, any error occurring in a <span class="application">PL/pgSQL</span>
function aborts execution of the function and the
surrounding transaction. You can trap errors and recover
from them by using a <code class="command">BEGIN</code> block with an
<code class="literal">EXCEPTION</code> clause. The syntax is an extension of the
normal syntax for a <code class="command">BEGIN</code> block:
</p><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
[<span class="optional"> DECLARE
<em class="replaceable"><code>declarations</code></em> </span>]
BEGIN
<em class="replaceable"><code>statements</code></em>
EXCEPTION
WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN
<em class="replaceable"><code>handler_statements</code></em>
[<span class="optional"> WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN
<em class="replaceable"><code>handler_statements</code></em>
... </span>]
END;
</pre><p>
</p><p>
If no error occurs, this form of block simply executes all the
<em class="replaceable"><code>statements</code></em>, and then control passes
to the next statement after <code class="literal">END</code>. But if an error
occurs within the <em class="replaceable"><code>statements</code></em>, further
processing of the <em class="replaceable"><code>statements</code></em> is
abandoned, and control passes to the <code class="literal">EXCEPTION</code> list.
The list is searched for the first <em class="replaceable"><code>condition</code></em>
matching the error that occurred. If a match is found, the
corresponding <em class="replaceable"><code>handler_statements</code></em> are
executed, and then control passes to the next statement after
<code class="literal">END</code>. If no match is found, the error propagates out
as though the <code class="literal">EXCEPTION</code> clause were not there at all:
the error can be caught by an enclosing block with
<code class="literal">EXCEPTION</code>, or if there is none it aborts processing
of the function.
</p><p>
The <em class="replaceable"><code>condition</code></em> names can be any of
those shown in <a class="xref" href="errcodes-appendix.html" title="Appendix A. PostgreSQL Error Codes">Appendix A</a>. A category
name matches any error within its category. The special
condition name <code class="literal">OTHERS</code> matches every error type except
<code class="literal">QUERY_CANCELED</code> and <code class="literal">ASSERT_FAILURE</code>.
(It is possible, but often unwise, to trap those two error types
by name.) Condition names are
not case-sensitive. Also, an error condition can be specified
by <code class="literal">SQLSTATE</code> code; for example these are equivalent:
</p><pre class="programlisting">
WHEN division_by_zero THEN ...
WHEN SQLSTATE '22012' THEN ...
</pre><p>
</p><p>
If a new error occurs within the selected
<em class="replaceable"><code>handler_statements</code></em>, it cannot be caught
by this <code class="literal">EXCEPTION</code> clause, but is propagated out.
A surrounding <code class="literal">EXCEPTION</code> clause could catch it.
</p><p>
When an error is caught by an <code class="literal">EXCEPTION</code> clause,
the local variables of the <span class="application">PL/pgSQL</span> function
remain as they were when the error occurred, but all changes
to persistent database state within the block are rolled back.
As an example, consider this fragment:
</p><pre class="programlisting">
INSERT INTO mytab(firstname, lastname) VALUES('Tom', 'Jones');
BEGIN
UPDATE mytab SET firstname = 'Joe' WHERE lastname = 'Jones';
x := x + 1;
y := x / 0;
EXCEPTION
WHEN division_by_zero THEN
RAISE NOTICE 'caught division_by_zero';
RETURN x;
END;
</pre><p>
When control reaches the assignment to <code class="literal">y</code>, it will
fail with a <code class="literal">division_by_zero</code> error. This will be caught by
the <code class="literal">EXCEPTION</code> clause. The value returned in the
<code class="command">RETURN</code> statement will be the incremented value of
<code class="literal">x</code>, but the effects of the <code class="command">UPDATE</code> command will
have been rolled back. The <code class="command">INSERT</code> command preceding the
block is not rolled back, however, so the end result is that the database
contains <code class="literal">Tom Jones</code> not <code class="literal">Joe Jones</code>.
</p><div class="tip"><h3 class="title">Tip</h3><p>
A block containing an <code class="literal">EXCEPTION</code> clause is significantly
more expensive to enter and exit than a block without one. Therefore,
don't use <code class="literal">EXCEPTION</code> without need.
</p></div><div class="example" id="PLPGSQL-UPSERT-EXAMPLE"><p class="title"><strong>Example 43.2. Exceptions with <code class="command">UPDATE</code>/<code class="command">INSERT</code></strong></p><div class="example-contents"><p>
This example uses exception handling to perform either
<code class="command">UPDATE</code> or <code class="command">INSERT</code>, as appropriate. It is
recommended that applications use <code class="command">INSERT</code> with
<code class="literal">ON CONFLICT DO UPDATE</code> rather than actually using
this pattern. This example serves primarily to illustrate use of
<span class="application">PL/pgSQL</span> control flow structures:
</p><pre class="programlisting">
CREATE TABLE db (a INT PRIMARY KEY, b TEXT);
CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
LOOP
-- first try to update the key
UPDATE db SET b = data WHERE a = key;
IF found THEN
RETURN;
END IF;
-- not there, so try to insert the key
-- if someone else inserts the same key concurrently,
-- we could get a unique-key failure
BEGIN
INSERT INTO db(a,b) VALUES (key, data);
RETURN;
EXCEPTION WHEN unique_violation THEN
-- Do nothing, and loop to try the UPDATE again.
END;
END LOOP;
END;
$$
LANGUAGE plpgsql;
SELECT merge_db(1, 'david');
SELECT merge_db(1, 'dennis');
</pre><p>
This coding assumes the <code class="literal">unique_violation</code> error is caused by
the <code class="command">INSERT</code>, and not by, say, an <code class="command">INSERT</code> in a
trigger function on the table. It might also misbehave if there is
more than one unique index on the table, since it will retry the
operation regardless of which index caused the error.
More safety could be had by using the
features discussed next to check that the trapped error was the one
expected.
</p></div></div><br class="example-break" /><div class="sect3" id="PLPGSQL-EXCEPTION-DIAGNOSTICS"><div class="titlepage"><div><div><h4 class="title">43.6.8.1. Obtaining Information about an Error <a href="#PLPGSQL-EXCEPTION-DIAGNOSTICS" class="id_link">#</a></h4></div></div></div><p>
Exception handlers frequently need to identify the specific error that
occurred. There are two ways to get information about the current
exception in <span class="application">PL/pgSQL</span>: special variables and the
<code class="command">GET STACKED DIAGNOSTICS</code> command.
</p><p>
Within an exception handler, the special variable
<code class="varname">SQLSTATE</code> contains the error code that corresponds to
the exception that was raised (refer to <a class="xref" href="errcodes-appendix.html#ERRCODES-TABLE" title="Table A.1. PostgreSQL Error Codes">Table A.1</a>
for a list of possible error codes). The special variable
<code class="varname">SQLERRM</code> contains the error message associated with the
exception. These variables are undefined outside exception handlers.
</p><p>
Within an exception handler, one may also retrieve
information about the current exception by using the
<code class="command">GET STACKED DIAGNOSTICS</code> command, which has the form:
</p><pre class="synopsis">
GET STACKED DIAGNOSTICS <em class="replaceable"><code>variable</code></em> { = | := } <em class="replaceable"><code>item</code></em> [<span class="optional"> , ... </span>];
</pre><p>
Each <em class="replaceable"><code>item</code></em> is a key word identifying a status
value to be assigned to the specified <em class="replaceable"><code>variable</code></em>
(which should be of the right data type to receive it). The currently
available status items are shown
in <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES" title="Table 43.2. Error Diagnostics Items">Table 43.2</a>.
</p><div class="table" id="PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES"><p class="title"><strong>Table 43.2. Error Diagnostics Items</strong></p><div class="table-contents"><table class="table" summary="Error Diagnostics Items" border="1"><colgroup><col class="col1" /><col class="col2" /><col class="col3" /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal">RETURNED_SQLSTATE</code></td><td><code class="type">text</code></td><td>the SQLSTATE error code of the exception</td></tr><tr><td><code class="literal">COLUMN_NAME</code></td><td><code class="type">text</code></td><td>the name of the column related to exception</td></tr><tr><td><code class="literal">CONSTRAINT_NAME</code></td><td><code class="type">text</code></td><td>the name of the constraint related to exception</td></tr><tr><td><code class="literal">PG_DATATYPE_NAME</code></td><td><code class="type">text</code></td><td>the name of the data type related to exception</td></tr><tr><td><code class="literal">MESSAGE_TEXT</code></td><td><code class="type">text</code></td><td>the text of the exception's primary message</td></tr><tr><td><code class="literal">TABLE_NAME</code></td><td><code class="type">text</code></td><td>the name of the table related to exception</td></tr><tr><td><code class="literal">SCHEMA_NAME</code></td><td><code class="type">text</code></td><td>the name of the schema related to exception</td></tr><tr><td><code class="literal">PG_EXCEPTION_DETAIL</code></td><td><code class="type">text</code></td><td>the text of the exception's detail message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_HINT</code></td><td><code class="type">text</code></td><td>the text of the exception's hint message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_CONTEXT</code></td><td><code class="type">text</code></td><td>line(s) of text describing the call stack at the time of the
exception (see <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK" title="43.6.9. Obtaining Execution Location Information">Section 43.6.9</a>)</td></tr></tbody></table></div></div><br class="table-break" /><p>
If the exception did not set a value for an item, an empty string
will be returned.
</p><p>
Here is an example:
</p><pre class="programlisting">
DECLARE
text_var1 text;
text_var2 text;
text_var3 text;
BEGIN
-- some processing which might cause an exception
...
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS text_var1 = MESSAGE_TEXT,
text_var2 = PG_EXCEPTION_DETAIL,
text_var3 = PG_EXCEPTION_HINT;
END;
</pre><p>
</p></div></div><div class="sect2" id="PLPGSQL-CALL-STACK"><div class="titlepage"><div><div><h3 class="title">43.6.9. Obtaining Execution Location Information <a href="#PLPGSQL-CALL-STACK" class="id_link">#</a></h3></div></div></div><p>
The <code class="command">GET DIAGNOSTICS</code> command, previously described
in <a class="xref" href="plpgsql-statements.html#PLPGSQL-STATEMENTS-DIAGNOSTICS" title="43.5.5. Obtaining the Result Status">Section 43.5.5</a>, retrieves information
about current execution state (whereas the <code class="command">GET STACKED
DIAGNOSTICS</code> command discussed above reports information about
the execution state as of a previous error). Its <code class="literal">PG_CONTEXT</code>
status item is useful for identifying the current execution
location. <code class="literal">PG_CONTEXT</code> returns a text string with line(s)
of text describing the call stack. The first line refers to the current
function and currently executing <code class="command">GET DIAGNOSTICS</code>
command. The second and any subsequent lines refer to calling functions
further up the call stack. For example:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION outer_func() RETURNS integer AS $$
BEGIN
RETURN inner_func();
END;
$$ LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION inner_func() RETURNS integer AS $$
DECLARE
stack text;
BEGIN
GET DIAGNOSTICS stack = PG_CONTEXT;
RAISE NOTICE E'--- Call Stack ---\n%', stack;
RETURN 1;
END;
$$ LANGUAGE plpgsql;
SELECT outer_func();
NOTICE: --- Call Stack ---
PL/pgSQL function inner_func() line 5 at GET DIAGNOSTICS
PL/pgSQL function outer_func() line 3 at RETURN
CONTEXT: PL/pgSQL function outer_func() line 3 at RETURN
outer_func
------------
1
(1 row)
</pre><p>
</p><p>
<code class="literal">GET STACKED DIAGNOSTICS ... PG_EXCEPTION_CONTEXT</code>
returns the same sort of stack trace, but describing the location
at which an error was detected, rather than the current location.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql-statements.html" title="43.5. Basic Statements">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html" title="Chapter 43. PL/pgSQL — SQL Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-cursors.html" title="43.7. Cursors">Next</a></td></tr><tr><td width="40%" align="left" valign="top">43.5. Basic Statements </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 43.7. Cursors</td></tr></table></div></body></html>
|
