使用 CTE 在 MySQL 中更新或删除

Question

新版本MySQL,8.0,现在支持Common Table Expressions.

根据手册：

A WITH clause is permitted at the beginning of SELECT, UPDATE, and DELETE statements:

WITH ... SELECT ...
WITH ... UPDATE ...
WITH ... DELETE ...

所以，我想，鉴于以下 table：

ID lastName firstName
----------------------
1  Smith    Pat
2  Smith    Pat
3  Smith    Bob

我可以使用以下查询：

;WITH ToDelete AS 
(
   SELECT ID,
          ROW_NUMBER() OVER (PARTITION BY lastName, firstName ORDER BY ID) AS rn
   FROM mytable
)   
DELETE FROM ToDelete

为了从 table 中删除重复项，就像我在 SQL Server 中所做的那样。

原来我错了。当我尝试从 MySQL Workbench 执行 DELETE 语句时，出现错误：

Error Code: 1146. Table 'todelete' doesn't exist

当我尝试使用 CTE 执行 UPDATE 时，我也收到错误消息。

所以，我的问题是，如何在 MySQL 中的 UPDATE 或 DELETE 语句的上下文中使用 WITH 子句（如8.0 版本手册)?

Answer 1

这似乎是 MySQL 8.x 中已发布的错误。来自这个bug report:

In the 2015 version of the SQL standard, a CTE cannot be defined in UPDATE; MySQL allows it but makes the CTE read-only (we're updating the documentation now to mention this). This said, one could use a view instead of the CTE; then the view may be updatable, but due to the presence of window functions it is materialized into a temporary table (it is not merged) so is not updatable (we're going to mention it in the doc as well).

All the above applies to DELETE too.

如果您遵循上述错误 link，您将看到建议使用 CTE 的变通方法，但它涉及将 CTE 与原始目标 table 一对一地连接起来映射。根据您的示例，这是一揽子删除，不清楚您需要什么解决方法，继续使用 CTE 进行删除。

Answer 2

由于CTE不是updatable，删除行需要参考原文table。我认为您正在寻找这样的东西：

WITH ToDelete AS 
(
   SELECT ID,
          ROW_NUMBER() OVER (PARTITION BY lastName, firstName ORDER BY ID) AS rn
   FROM mytable
)   
DELETE FROM mytable USING mytable JOIN ToDelete ON mytable.ID = ToDelete.ID
WHERE ToDelete.rn > 1;

使用 CTE 在 MySQL 中更新或删除

Use a CTE to UPDATE or DELETE in MySQL

mysql

common-table-expression

sql-update

sql-delete

mysql-8.0