SQL 删除重复记录，只保留一条记录

//删除用户 根据用户名，并且不包括最小ID
delete from users where username in (
         --根据用户名称排序，大于1
    select username from users group by username having count(username) > 1

 ) and Id not in (
        --根据用户名排序，获取最小ID
    select min(Id) from users group by username having count(username) > 1
);