I have very simple query like this:
SELECT * FROM `all_conversations` WHERE `deleted_1` != '1';
WHERE `deleted_1` != 'NULL'
AND `deleted_1` != 23
SELECT * FROM all_conversations WHERE deleted_1 <> 1 OR deleted_1 IS NULL
NULL values need special treatment: http://dev.mysql.com/doc/refman/5.1/en/working-with-null.html
I'd suggest using the diamond operator (
<>) in favor of
!= as the first one is valid SQL and the second one is a MySQL addition.