【mysql】不常用語法

1. is Null
SELECT * FROM user WHERE address is Null

2.is not Null
SELECT * FROM user WHERE address is not Null

3.not like
SELECT * FROM user WHERE address not like '_中%'

4.view 建立及移除暫存資料表
create view tmp as SELECT * FROM user WHERE address is Null
drop view tmp

5.distinct 重複的不計
SELECT count(distinct address) FROM user WHERE address is Null