Re: Variable value doesn't stay "Null"

Assuming that column MY_TABLE.MY_NUMERIC_FIELD allows NULLs: INSERT INTO MY_TABLE (MY_NUMERIC_FIELD, MY_OTHER_FIELD) VALUES ('', 'some_other_value') will insert a 0 into the column MY_NUMERIC_FIELD in MySQL and many other databases. To insert NULL, the SQL must read INSERT INTO MY_TABLE (MY_NUMERIC_FIELD, MY_OTHER_FIELD) VALUES (NULL, 'some_other_value') Hence when you build the SQL statement in PHP, check the value that is to be inserted into MY_NUMERIC_FIELD. If it is NULL as per your requirement, use the second form of SQL. You've said is_null($my_form_variable) returned FALSE though as per your requirement it should have been NULL. Try using empty(): if (empty($my_form_variable) || ! is_numeric($my_form_variable)) { $value_for_sql = 'NULL'; } else { $value_for_sql = $my_form_variable; } $sql = "INSERT INTO MY_TABLE (MY_NUMERIC_FIELD, MY_OTHER_FIELD) VALUES ($value_for_sql, '$my_other_form_variable')"; mysql_execute($sql); /* etc */ Hope this helps!