从MySQL中删除COUNT(*)
作者:互联网
好的,所以这里已有几个帖子,网上还有更少的帖子.我真的尝试了每一个,无法得到任何工作.希望有人在这里可以怜悯我:)
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)
我最接近找到可以执行此操作的代码如下所示.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,没有任何事情发生,所以我放弃它.
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)
解决方法:
如the manual所述:
Currently, you cannot delete from a table and select from the same table in a subquery.
我想你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;
标签:having,mysql,sql-delete,count 来源: https://codeday.me/bug/20191006/1861828.html