原始数据库 usename重复数据删除
第一步 找出username 字段有重复值 且count >1的username值
第二步 username字段有重复且count>1数据的最小id
显然就是以name为条件删除 id 不在第二步里面的所有数据 我们拼接sql语句
结果
#第一步 找出username 字段有重复值 且count >1的username值
select username as dname from employee group by username having count(username) > 1
-- 第二步 cv 上面的 在重复数据中找出最小id的数据
select min(id) as mid from employee group by username having count(username) > 1;
-- 拼接sql语句 删除第一步 名字里面的所有数据 除了各自id最小的数据 实现删除
sql语句 如下
#第一步 找出username 字段有重复值 且count >1的username值
select username as dname from employee group by username having count(username) > 1
-- 第二步 cv 上面的 在重复数据中找出最小id的数据
select min(id) as mid from employee group by username having count(username) > 1;
-- 拼接sql语句 删除第一步 名字里面的所有数据 除了各自id最小的数据 实现删除
delete from employee
where
username in (select pname from (select username as pname from employee group by username having count(username) > 1) a)
and
id not in (select pid from (select min(id) as pid from employee group by username having count(username) > 1 ) b)
-- 完事 设置表单username唯一
alter table employee add unique(username);