10.18.NULL | ||||
10.18.1. | NULL means 'a missing unknown value' | |||
10.18.2. | Use the IS NULL and IS NOT NULL operators for NULL value | |||
10.18.3. | In MySQL, 0 or NULL means false and anything else means true. | |||
10.18.4. | Two NULL values are regarded as equal in a GROUP BY | |||
10.18.5. | NULL values are presented first if you do ORDER BY ... ASC | |||
10.18.6. | NULL values are presented last if you do ORDER BY ... DESC | |||
10.18.7. | Use 0 and '' is not NULL |