13

好的，所以这里已经有几个帖子了，网上的帖子更少了。我实际上已经尝试了其中的每一个，但都无法正常工作。希望这里的人可以同情我:)

这是我正在使用的数据。我想删除所有这些记录。

SELECT
part_desc, count(*) as rec_num
FROM ag_master
GROUP BY part_desc HAVING COUNT(*) > 1000;

+--------------------------------------+---------+
| part_desc                            | rec_num |
+--------------------------------------+---------+
| SILICON DELAY LINE, TRUE OUTPUT      |    1092 |
| LOADABLE PLD                         |    1401 |
| 8-BIT, FLASH, 8 MHz, MICROCONTROLLER |    1411 |
| FPGA                                 |    1997 |
| 8-BIT, MROM, 8 MHz, MICROCONTROLLER  |    3425 |
+--------------------------------------+---------+
5 rows in set (0.00 sec)

我找到的最接近的代码如下所示。语法检查正常并运行，但它似乎只是挂起数据库。我让它运行了长达 10 分钟，但什么也没发生，所以我中止了它。

DELETE
FROM ag_master
WHERE part_id IN (
  SELECT part_id
  FROM ag_master
  GROUP BY part_desc
  HAVING COUNT(*) > 1000
);

这是 tmp 表上的解释计划

mysql> EXPLAIN SELECT * FROM ag_master WHERE part_desc IN (SELECT part_desc FROM tmp);
+----+--------------------+-----------+--------+---------------+------+---------+------+--------+-------------+
| id | select_type        | table     | type   | possible_keys | key  | key_len | ref  | rows   | Extra       |
+----+--------------------+-----------+--------+---------------+------+---------+------+--------+-------------+
|  1 | PRIMARY            | ag_master | ALL    | NULL          | NULL | NULL    | NULL | 177266 | Using where |
|  2 | DEPENDENT SUBQUERY | tmp       | system | NULL          | NULL | NULL    | NULL |      1 |             |
+----+--------------------+-----------+--------+---------------+------+---------+------+--------+-------------+
2 rows in set (0.00 sec)
4

2 回答 2

19

如手册所述：

目前，您不能在子查询中从表中删除并从同一个表中选择。

我认为您必须通过临时表执行此操作：

CREATE TEMPORARY TABLE temp
  SELECT   part_desc
  FROM     ag_master
  GROUP BY part_desc
  HAVING   COUNT(*) > 1000;

DELETE FROM ag_master WHERE part_desc IN (SELECT part_desc FROM temp);

DROP TEMPORARY TABLE temp;
于 2012-05-11T15:55:57.253 回答
9

另一种选择是使用内部连接来过滤结果：

DELETE
    ag_master.*
FROM
    ag_master 

    INNER JOIN 
    (
        SELECT 
            part_id
        FROM 
            ag_master
        GROUP BY 
            part_desc
        HAVING COUNT(*) > 1000
    )AS todelete ON
            todelete.part_id = ag_master.part_id
于 2015-01-21T14:42:21.587 回答