pgsql 8.4 "not" + "is contained by" operators return wrong result - Mailing list pgsql-bugs

Description:

By pgsql 8.4 I have the following bug:

If the haystack array is null (for example by empty result of array_agg) by is contained by, and you use it with negation, the the result is false instead of true.

Reproduce:

The following query returns nothing, but it should return 1.

SELECT 1 FROM NOT(ARRAY[1] <@ NULL);  

Workaround:

SELECT 1 FROM (haystack IS NULL OR NOT(ARRAY[1] <@ haystack));