mysql双group_mysql-----group by 对多个字段进行分组

group by a：将所有具有相同a字段值的记录放到一个分组里；

group by a,b ：将所有具有相同a字段值和b字段值的记录放到一个分组里

count( case when sex='1' then '男') as count1,

count( case when sex='2' then '女') as count2,

使用语法：

SELECT

CASEWHEN salary <= 500THEN'1'

WHEN salary > 500AND salary <= 600THEN'2'

WHEN salary > 600AND salary <= 800THEN'3'

WHEN salary > 800AND salary <= 1000THEN'4'

ELSENULLENDsalary_class, -- 别名命名

COUNT(*)FROM Table_A

GROUPBY

CASEWHEN salary <= 500THEN'1'

WHEN salary > 500AND salary <= 600THEN'2'

WHEN salary > 600AND salary <= 800THEN'3'

WHEN salary > 800AND salary <= 1000THEN'4'

ELSENULLEND;