where

运算符	说明
=	等于
!=	不等于，某些数据库系统也写作 <>
>	大于
<	小于
>=	大于或等于
<=	小于或等于
BETWEEN … AND …	介于某个范围之内，例：WHERE age BETWEEN 20 AND 30
NOT BETWEEN …AND …	不在某个范围之内
IN(项1,项2,…)	在指定项内，例：WHERE city IN('beijing','shanghai')
NOT IN(项1,项2,…)	不在指定项内
LIKE	搜索匹配，常与模式匹配符配合使用
NOT LIKE	LIKE的反义
IS NULL	空值判断符
IS NOT NULL	非空判断符
NOT、AND、OR	逻辑运算符，分别表示否、并且、或，用于多个逻辑连接。优先级：NOT > AND > OR
%	模式匹配符，表示任意字串，例：WHERE username LIKE '%user'
REGEXP	模式匹配符，表示任意字串，例：WHERE username LIKE '%user'

--测试条件
a = 'test'
table.a = 'test' and table.b != 'test' 
a > '3' or b < '5' or c >= '4' or d <= '5' 
a > '3' and (b < '5' or c = 10)
a > '3' and (b < '5' or c = 10 and (d = 10 or e = 13))
a like '%test%' or b is null  and c is not null
a not in (3,4,5) and b in (3,4,5)
a between '1' and '10' and b not bebween '1' and '13'
a REGEXP "^fo"