Hello all,
I apologize for the wide distribution but we recently ran into an
interesting behaviour using PostgreSQL 8.0.3 and did not know whether
this was a bug or intended behaviour.
When an IN clause contains a NULL value the entire in clause is considered as being false, thus no records are returned.
Why doesn't IN evaluate NULL as a value?
so for example:
SELECT count(*) FROM test WHERE key NOT IN ('something');
returns the count of rows...
where
SELECT count(*) FROM test WHERE key NOT IN ('something', NULL);
does not. table test does not have any NULL values in the key column.
the query plans follow...
mazu=# EXPLAIN ANALYZE SELECT count(*) FROM test WHERE key NOT IN ('something');
QUERY
PLAN
------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=100000022.44..100000022.44 rows=1 width=0) (actual time=0.664..0.665 rows=1 loops=1)
-> Seq Scan on test
(cost=100000000.00..100000020.38 rows=826 width=0) (actual
time=0.030..0.349 rows=168 loops=1)
Filter: (("key")::text <> 'something'::text)
Total runtime: 0.826 ms
(4 rows)
mazu=# EXPLAIN ANALYZE SELECT count(*) FROM test WHERE key NOT IN ('something', NULL);
QUERY
PLAN
------------------------------------------------------------------------------------------------------------
Aggregate (cost=100000022.44..100000022.44 rows=1 width=0) (actual time=0.027..0.029 rows=1 loops=1)
-> Result (cost=100000000.00..100000020.38
rows=826 width=0) (actual time=0.002..0.002 rows=0 loops=1)
One-Time Filter: NULL::boolean
-> Seq Scan
on test (cost=100000000.00..100000020.38 rows=826 width=0) (never
executed)
Filter: (("key")::text <> 'something'::text)
Total runtime: 0.110 ms
(6 rows)
--
Joe Maldonado
