why this MYSQL query return null?

Question

Why does this query always return NULL?

SELECT (Supervisor IS NULL) = (Supervisor = NULL) FROM Salespeople

is it because we specify the second half with equal to null ?

possible duplicate of [SQL is null and = null](http://stackoverflow.com/questions/9581745/sql-is-null-and-null) — Clockwork-Muse, Dec 07 '14 at 13:28

Yigitalp Ertem · Answer 1 · 2014-12-07T11:35:05.857

2

Supervisor IS NULL returns TRUE or FALSE.

Supervisor = NULL always returns NULL.

Thus, TRUE = NULL or FALSE = NULL will always return NULL.

That's why your query will return NULL rows whose count will be the total row-count of your table.

edited Dec 07 '14 at 11:35

answered Dec 07 '14 at 11:28

Yigitalp Ertem

1 Answers1