MySQL操作 UPDATE、SELECT、UNION、IN、DISTINCT

update 更新

所有人的年龄加一：update user set age=age+1;
只更新某个： update user set age=age+1 where name='zhang san';

select查询

select * from user;//一般不建议使用通配符
select name,age,sex from user;//根据键查找
select name,age,sex from user where sex='M' and age>=20 and age<=25;
select name,age,sex from user where sex='M' and age between 20 and 25;
select name,age,sex from user where sex='W' or age>=22;
select name,age,sex from user where name like "zhang%";
select name,age,sex from user where name is not null;

联合查询 UNION

SELECT expression1, expression2, ... expression_n
FROM tables[WHERE conditions]
UNION [ALL | DISTINCT]
SELECT expression1, expression2, ... expression_n
FROM tables[WHERE conditions]

union默认去重，不用修饰distinct，all表示显示所有重复值

例如：

select name,age,sex from user where age >=21 union all select name,age,sex from user where sex='M';

注意:between是[ ]。like 部分匹配不加=，null not null使用is

带in子查询

select name,age,sex from user where age in (20,21);
select name,age,sex from user where age not in (20,21);

在一个区间内查找IN，不在这个区间内查找NOT IN.

去重

将年龄拿出来去重显示： select distinct age from user;