Why does MySQL allow to update a NOT NULL column to NULL?

Question

I'm running MySql in ubuntu 10.10. I created a table called 'employee' having 3 field names empno, name and salary. Inserted few entities. In the middle of the process i want to change salary attribute as 'NOT NULL'. I Alter the table as

ALTER TABLE employee MODIFY salary int(10) NOT NULL;

Query executed. I wanted to test by using command,

UPDATE employee SET salary=NULL;

Query OK, 15 rows affected, 15 warnings (0.06 sec)
Rows matched: 15  Changed: 15  Warnings: 15

also gave warnings " (Code 1048): Column 'salary' cannot be null "(Repeated for every row)

But when i saw my table , All salaries were Zeros('0').

Same queries result in error instead of warning in WINDOWS XP's MySql

I checked in both INNODB and MYISAM engines but same Result. Please help me to know what happened beside processing.

Answer 1

You must not have SQL_MODE set to strict on you ubuntu installation.

Issue

SET SQL_MODE='STRICT_ALL_TABLES'

or add

SQL_MODE='STRICT_ALL_TABLES'

under [mysqld] to your my.cnf on Ubuntu.