MySQL-14.DQL-分组查询
一.DQL-分组查询
-- 分组 group by
-- 1.根据性别分组,统计男性和女性员工的数量 - count(*)
select gender,count(*) from tb_emp group by gender;
-- 2.先查询入职日期在'2015-01-01'(包含)以前的员工,并对结果根据职位分组,获取员工数量大于等于2的职位
select job,count(*) from tb_emp where entrydate <= '2015-01-01' group by job having count(*) >= 2;