mysql-group by分组用法

sql执行顺序

select 查询列表         -- 7
from 表                -- 1
join 表2               -- 2
on 连接条件             -- 3
where 筛选条件          -- 4
group by 分组字段       -- 5
having 分组后的筛选     -- 6
order by 排序的字段     -- 8
limit offset, size;    -- 9

SELECT * FROM user_t

• group by + group_concat()

  select sex, group_concat(username) from user_t group by sex;
  

  

• group by可用于多个字段分组：多个字段完全一致为一组

  select sex, address, group_concat(username), group_concat(address) from user_t group by sex, address;
  

  

• group by + 聚合函数

  select sex,group_concat(age), SUM(age), COUNT(*), avg(age) from user_t group by sex;
  

  

• group by + having：用来过滤分组结果

  select age, group_concat(username),count(*) from user_t group by age HAVING count(*)=3;
  

  

mysql-group by分组用法