On Feb 26, 2010, at 0:55 , Дмитрий Фефелов wrote:
http://developer.postgresql.org/pgdocs/postgres/release-9-0.html
Performance section:
Simplify the forms foo <> true and foo <> false to foo = false and
foo = true during query optimization.
Will it work correct;ly when foo is NULL?
It shouldn't have any effect: NULL <> anything and NULL = anything is
NULL
SELECT arg1, arg2,
(arg1 <> arg2) AS "arg1 <> arg2",
(arg1 = arg2) AS "(arg1 = arg2)"
FROM (VALUES (TRUE, TRUE), (TRUE, FALSE),
(FALSE, TRUE), (FALSE, FALSE),
(NULL, TRUE), (NULL, FALSE)) AS bools (arg1, arg2)
ORDER BY arg1, arg2;
arg1 | arg2 | arg1 <> arg2 | (arg1 = arg2)
--------+------+--------------+---------------
f | f | f | t
f | t | t | f
t | f | t | f
t | t | f | t
(null) | f | (null) | (null)
(null) | t | (null) | (null)
(6 rows)
Michael Glaesemann
grzm seespotcode net
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