Question

我正在尝试这样的查询：

DELETE FROM term_hierarchy AS th
WHERE th.parent = 1015 AND th.tid IN (
    SELECT DISTINCT(th1.tid)
    FROM term_hierarchy AS th1
    INNER JOIN term_hierarchy AS th2 ON (th1.tid = th2.tid AND th2.parent != 1015)
    WHERE th1.parent = 1015
);

正如你可能知道的那样，如果同一个tid有其他父母，我想删除1015的父关系。但是，这会产生语法错误：

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AS th
WHERE th.parent = 1015 AND th.tid IN (
  SELECT DISTINCT(th1.tid)
  FROM ter' at line 1

我检查了文档，并自行运行子查询，这一切似乎都要检查。谁能弄清楚这里有什么问题？

更新：如下所述，MySQL不允许您删除的表在子查询中用于该条件。

Answer 1

对于那些在使用子查询时发现这个问题想要删除的人，我给你留下了这个例子来说明MySQL（即使有些人似乎认为无法完成）：

DELETE e.*
FROM tableE e
WHERE id IN (SELECT id
             FROM tableE
             WHERE arg = 1 AND foo = 'bar');

会给你一个错误：

ERROR 1093 (HY000): You can't specify target table 'e' for update in FROM clause

但是这个查询：

DELETE e.*
FROM tableE e
WHERE id IN (SELECT id
             FROM (SELECT id
                   FROM tableE
                   WHERE arg = 1 AND foo = 'bar') x);

可以正常使用：

Query OK, 1 row affected (3.91 sec)

将子查询包含在另一个子查询中（此处名为x），MySQL将很乐意按您的要求进行操作。

Answer 2

您无法指定要删除的目标表。

解决方法

create table term_hierarchy_backup (tid int(10)); <- check data type

insert into term_hierarchy_backup 
SELECT DISTINCT(th1.tid)
FROM term_hierarchy AS th1
INNER JOIN term_hierarchy AS th2 ON (th1.tid = th2.tid AND th2.parent != 1015)
WHERE th1.parent = 1015;

DELETE FROM term_hierarchy AS th
WHERE th.parent = 1015 AND th.tid IN (select tid from term_hierarchy_backup);

Answer 3

别名应包含在DELETE关键字后面：

DELETE th
FROM term_hierarchy AS th
WHERE th.parent = 1015 AND th.tid IN 
(
    SELECT DISTINCT(th1.tid)
    FROM term_hierarchy AS th1
    INNER JOIN term_hierarchy AS th2 ON (th1.tid = th2.tid AND th2.parent != 1015)
    WHERE th1.parent = 1015
);

Answer 4

您需要在delete语句中再次引用别名，例如：

DELETE th FROM term_hierarchy AS th
....

As outlined here in MySQL docs.

Answer 5

我以稍微不同的方式接近它，它对我有用;

我需要从引用secure_links表的表中删除conditions，其中不再有任何条件行。一个看家脚本基本上。这给了我错误 - 您无法指定要删除的目标表。

所以在这里寻找灵感我想出了下面的查询，它运作得很好。这是因为它创建了一个临时表sl1，用作DELETE的引用。

DELETE FROM `secure_links` WHERE `secure_links`.`link_id` IN 
            (
            SELECT
                `sl1`.`link_id` 
            FROM 
                (
                SELECT 

                    `sl2`.`link_id` 

                FROM 
                    `secure_links` AS `sl2` 
                    LEFT JOIN `conditions` ON `conditions`.`job` = `sl2`.`job` 

                WHERE 

                    `sl2`.`action` = 'something' AND 
                    `conditions`.`ref` IS NULL 
                ) AS `sl1`
            )

适合我。

Answer 6

不是删除中的“in”子句......如果从子查询中返回大量值，效率极低吗？不确定为什么你不会只是内部（或右）从要删除的ID的子查询中反对原始表，而不是我们“in（子查询）”。？

DELETE T FROM Target AS T
RIGHT JOIN (full subquery already listed for the in() clause in answers above) ` AS TT ON (TT.ID = T.ID)

也许它在“MySQL不允许它”中得到解答，但是，它对我来说工作正常提供我确保完全澄清要删除的内容（DELETE T FROM Target AS T）。 Delete with Join in MySQL澄清了DELETE / JOIN问题。

Answer 7

如果您想使用2个查询执行此操作，则可以始终执行与此类似的操作：

1）从表中抓取ID：

SELECT group_concat(id) as csv_result FROM your_table WHERE whatever = 'test' ...

然后用鼠标/键盘或编程语言将结果复制到以下XXX：

2) DELETE FROM your_table WHERE id IN ( XXX )

也许你可以在一个查询中执行此操作，但这是我更喜欢的。

Answer 8

@ CodeReaper，@ BennyHill：它按预期工作。

但是，我想知道表中具有数百万行的时间复杂度吗？显然，要在正确索引的表上拥有5k条记录，大约要花费5ms才能执行。

我的查询

SET status = '1'
WHERE id IN (
    SELECT id
    FROM (
      SELECT c2.id FROM clusters as c2
      WHERE c2.assign_to_user_id IS NOT NULL
        AND c2.id NOT IN (
         SELECT c1.id FROM clusters AS c1
           LEFT JOIN cluster_flags as cf on c1.last_flag_id = cf.id
           LEFT JOIN flag_types as ft on ft.id = cf.flag_type_id
         WHERE ft.slug = 'closed'
         )
      ) x)```

Or is there something we can improve on my query above?

Answer 9

您可以通过这种方式在删除语句上使用别名

DELETE  th.*
FROM term_hierarchy th
INNER JOIN term_hierarchy th2 ON (th1.tid = th2.tid AND th2.parent != 1015)
WHERE th.parent = 1015;

MySQL将DELETE FROM与子查询作为条件

9 个答案: