Re: Coalesce bug ?

Hi,

Please test this script on a PostgreSQL 9.1.6,

create or replace function ps3(a int) returns int as $$ BEGIN
RAISE WARNING 'Call ps3(%)=%',$1,$1; RETURN $1::int;
END; $$ LANGUAGE plpgsql STRICT IMMUTABLE;
SELECT ps3(1);
SELECT ps3(2);
select coalesce( (select ps3(1)), (SELECT ps3(2)) );
explain (verbose, analyze, buffers) select coalesce( (select ps3(1)), (SELECT ps3(2)) );
select coalesce( ps3(1), ps3(2) );

The result will be

[postgres(at)]test=# create or replace function ps3(a int) returns int as $$ BEGIN
test$# RAISE WARNING 'Call ps3(%)=%',$1,$1; RETURN $1::int;
test$# END; $$ LANGUAGE plpgsql STRICT IMMUTABLE;
CREATE FUNCTION
Temps : 13,232 ms
[postgres(at)]test=# SELECT ps3(1);
WARNING: Call ps3(1)=1
ps3
-----
1
(1 ligne)

Temps : 0,975 ms
[postgres(at)]test=# SELECT ps3(2);
WARNING: Call ps3(2)=2
ps3
-----
2
(1 ligne)

Temps : 0,473 ms
[postgres(at)]test=# select coalesce( (select ps3(1)), (SELECT ps3(2)) );
WARNING: Call ps3(1)=1
WARNING: Call ps3(2)=2
coalesce
----------
1
(1 ligne)

Temps : 0,681 ms
[postgres(at)]test=# explain (verbose, analyze, buffers) select coalesce( (select ps3(1)), (SELECT ps3(2)) );
WARNING: Call ps3(1)=1
WARNING: Call ps3(2)=2
QUERY PLAN

--------------------------------------------------------------------------------
------------
Result (cost=0.02..0.03 rows=1 width=0) (actual time=0.004..0.004 rows=1 loops
=1)
Output: COALESCE($0, $1)
InitPlan 1 (returns $0)
-> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.000..0.000 rows
=1 loops=1)
Output: 1
InitPlan 2 (returns $1)
-> Result (cost=0.00..0.01 rows=1 width=0) (never executed)
Output: 2
Total runtime: 0.022 ms
(9 lignes)

Temps : 0,774 ms
[postgres(at)]test=# select coalesce( ps3(1), ps3(2) );
WARNING: Call ps3(1)=1
coalesce
----------
1
(1 ligne)

Temps : 0,562 ms
[postgres(at)]test=#

There is a bug !

Thank you for the documentation link, but it does not help me.

JG