"Michael Pilling" <michael.pill...@dsto.defence.gov.au> wrote: > A reasonable programmer would expect != NULL, <> NULL and IS NOT > NULL to be synonyms. Only if that programmer was not aware of the SQL standard and had not worked much with a standard-conforming database. NULL is conceptually intended to indicate "unknown" or "not applicable". If you have a person table with a date_of_birth column, which contains NULL for a number of rows for which the date of birth is unknown, can you say that all such people have the same date of birth? No; for any such person, the result of comparing their date of birth to anyone else's (whether or not the other one is NULL) is UNKNOWN. You might want to read up on IS [NOT] DISTINCT FROM. In the SQL language, while NULL is not known to be equal to NULL, you *can* say that NULL IS NOT DISTINCT FROM NULL. This is most definitely not a bug in the software. The documentation does cover it here: http://www.postgresql.org/docs/9.0/interactive/functions-comparison.html Is there something you would add to that? -Kevin
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