难点：自己不能删除自己，要进行多次转换
1.查询表中数据
select * from test ;
| id | name | value |
| 1 | p | p |
| 2 | p | p |
| 3 | pp | pp |
| 4 | pp | pp |
| 5 | ppp | ppp |
| 6 | ppp | ppp |
| 7 | pppp | pppp |
| 8 | pppp | pppp |
执行操作后
select * from test ;
| id | name | value |
| 1 | p | p |
| 3 | pp | pp |
| 5 | ppp | ppp |
| 7 | pppp | pppp |
2.操作
delete a from test a left join( select (id) from test group by name,value )b on a.id=b.id where b.id is null ;
delete from test where id not in
(
select a.id from
(
select id from test a where exists
(
select id from test b group by name,value HAVING count(b.id)> 1
) group by name,value
)a
);
说明，若未指定id是查询中最大的id还是最小的id，默认为id最小的
select id from test b group by name,value HAVING count(b.id)> 1
| id |
| 1 |
| 3 |
| 5 |
| 7 |
3.查询相同数据的比较大的id值
select max(id) from test group by name,value having count(id)>1;
| max(id) |
| 2 |
| 4 |
| 6 |
| 8 |