AND field NOT IN(NULL) returns an empty set [duplicate]

Answer 1

x NOT IN (...) is defined as a series of comparisons between x and each of the values returned by the subquery. SQL uses three-value logic, for which the three possible values of a logical expression are true, false or unknown. Comparison of a value to a NULL is unknown and if any one of those NOT IN comparisons is unknown then the result is also deemed to be unknown.

Answer 2

dont compare NULL with NULL

you need to specify IS NOT NULL here

Answer 3

Comparing with null is always a bad idea. Even NULL = NULL or NULL <> NULL will return NULL.

Use IS NOT NULL insetad

In your case the query is identical to:

select p.iuser_id,p.produit_id from portefeuille p
WHERE produit_id=48
AND p.iuser_id <> NULL;

and the value of p.iuser_id <> NULL will be NULL regardless of the value of p.isuer_id and this explains why it returns an empty set!

Answer 4

Any comparison to NULL, with the exception of is null and is not null, returns NULL which is interpreted as false for boolean purposes. This is standard behavior for all databaes.

If you want to do a comparison within a set of values, here are two options:

where coalesce(produit_id, -1) not in (-1, . . . .)

This assumes that -1 is an invalid value for the id. Or, you can do an explicit comparison:

where produit_id is not null and produit_id not in ( . . . )