Michael Fuhr wrote:
Why does the first query below return the same value for each row
while the second query returns random values? Planner optimization?
I assume it is due to some kind of flattening in the planner, but it is
totally unrelated to ARRAY(subquery):
regression=# SELECT (SELECT random()) as f FROM generate_series(1, 5);
f
-------------------
0.752416231088534
0.752416231088534
0.752416231088534
0.752416231088534
0.752416231088534
(5 rows)
regression=# SELECT (SELECT random() + 0 * f) as f FROM
generate_series(1, 5) as t(f);
f
-------------------
0.176055165555354
0.608546747178094
0.55303416240636
0.127355110425202
0.21671894063089
(5 rows)
Here's another example:
regression=# create table t1(f text);
CREATE TABLE
regression=# insert into t1 values('0');
INSERT 17366 1
regression=# insert into t1 values('0');
INSERT 17367 1
regression=# insert into t1 values('0');
INSERT 17368 1
regression=# SELECT (SELECT timeofday()::timestamp + f::interval) as f
FROM t1;
f
----------------------------
2005-08-16 16:38:12.738215
2005-08-16 16:38:12.738292
2005-08-16 16:38:12.738315
(3 rows)
regression=# SELECT (SELECT timeofday()::timestamp) as f FROM t1;
f
----------------------------
2005-08-16 16:35:33.100791
2005-08-16 16:35:33.100791
2005-08-16 16:35:33.100791
(3 rows)
This shows that it isn't related to use of an SRF either.
Joe
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