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|
mysql> select * from test1;
+------+------+
| id | c_id |
+------+------+
| 1 | 0013 |
| 2 | 0014 |
| 3 | 0013 |
| 4 | 0013 |
+------+------+
4 rows in set (0.06 sec)
mysql> delete t from test1 t left join
-> (select c_id,min(id) as min_id from test1 group by c_id) t1
-> on t.id=t1.min_id
-> where t1.min_id is null;
Query OK, 2 rows affected (0.06 sec)
mysql> select * from test1;
+------+------+
| id | c_id |
+------+------+
| 1 | 0013 |
| 2 | 0014 |
+------+------+
2 rows in set (0.00 sec)
|
有很多问题都需要使用相同表left join关联来处理。