根据其他表列更新表列

Question

我想更新表cases_proceedings，但是它将在其他表cases_attach_files中检查一些标准，即

SELECT cp.sno FROM cases_proceedings cp, cases_attach_files cf 
WHERE cp.`case_sno` = cf.`case_sno` AND cf.page_lbl_sno = 10 AND 
cp.`is_decided` = 0

但是，当我想更新第一个表的值并通过对子查询使用IN操作来搜索第一个表的sno时 ，如下所示：

UPDATE cases_proceedings 
     SET `is_decided` = 1 
WHERE sno IN(SELECT cp.sno FROM cases_proceedings cp, cases_attach_files cf 
WHERE cp.`case_sno` = cf.`case_sno` AND cf.page_lbl_sno = 10 AND 
cp.`is_decided` = 0);

它显示一个错误：

Error Code: 1093
You can't specify target table 'cases_proceedings' for update in FROM clause

我不知道该如何解决？

Answer 1

一种解决方法是将子查询包装在另一个子查询中：

UPDATE cases_proceedings 
SET is_decided = 1 
WHERE sno IN
(
    SELECT sno
    FROM
    (
        SELECT cp.sno
        FROM cases_proceedings cp
        INNER JOIN cases_attach_files cf 
            ON cp.case_sno = cf.case_sno AND
               cf.page_lbl_sno = 10 AND
               cp.is_decided = 0
    ) t
);

额外的子查询可解决该错误，因为它迫使MySQL实现包含联接的子查询。

Answer 2

根据文档 ，在MySQL中，您不能修改在SELECT部分​​中使用的同一表。

您可以将其包装在子查询中，也可以将两个表连接起来，如下所示：

UPDATE  cases_proceedings cp
        INNER JOIN cases_attach_files cf
            ON cp.case_sno = cf.case_sno
                AND cf.page_lbl_sno = 10 
                AND cp.is_decided = 0
SET     cp.is_decided = 1