Question

当我添加子查询时，

mysql更新语法似乎不起作用。更新语法上的子查询是否有限制？

不起作用：

    update books set imagename ='name' 
    where book_ID='(select book_ID from books order by book_ID desc limit 1)';

工作：

    update books set imagename ='name' 
    where book_ID='101';

Answer 1

MySQL使用正在更新的表确实对子查询有限制。所以不允许你这样做：

update books
    set imagename ='name' 
    where book_ID = (select book_ID from books order by book_ID desc limit 1);

相反，您可以这样做：

update books
    set imagename ='name' 
    order by book_ID desc
    limit 1;

以下是documentation中的解释：

通常，您无法修改表并从同一个表中进行选择在子查询中。例如，此限制适用于以下形式：
    DELETE FROM t WHERE ... (SELECT ... FROM t ...);
    UPDATE t ... WHERE col = (SELECT ... FROM t ...);
    {INSERT|REPLACE} INTO t (SELECT ... FROM t ...);
异常：如果在FROM子句中使用子查询来修改表，则前面的禁止不适用。例如：
    UPDATE t ... WHERE col = (SELECT * FROM (SELECT ... FROM t...) AS _t ...);
 Here the result from the subquery in the FROM clause is stored as a temporary table, so the relevant rows in t have already been
在更新到t时选择。

Answer 2

尝试此查询。

Update books
Set imagename = name"
Where book_ID In (
                Select T1.book_ID
                From books As T1
                Where T1.book_ID = '101'

                )

mysql更新子查询无法正常工作

2 个答案: