发布于 2015-08-27 14:27:49 | 182 次阅读 | 评论: 1 | 来源: PHPERZ
Mysql关系型数据库管理系统
MySQL是一个开放源码的小型关联式数据库管理系统，开发者为瑞典MySQL AB公司。MySQL被广泛地应用在Internet上的中小型网站中。由于其体积小、速度快、总体拥有成本低，尤其是开放源码这一特点，许多中小型网站为了降低网站总体拥有成本而选择了MySQL作为网站数据库。
按照MYSQL5.0文档的解释：我们不能在修改表A的同时在其子查询中使用到表A，但是可以通过在子查询中在嵌套一层针对表A的子查询，因为最里层的子查询产生的结果存在临时表中，与表A没有关系。
解决方法：把类似于 UPDATE t ... WHERE col = (SELECT ... FROM t ...); 改写成UPDATE t ... WHERE col = (SELECT (SELECT ... FROM t...) AS _t ...);即可。
文档原文：In general, you cannot modify a table and select from the same table in a subquery. For example, this limitation applies to statements of the following forms:
DELETE FROM t WHERE ... (SELECT ... FROM t ...);UPDATE t ... WHERE col = (SELECT ... FROM t ...);{INSERT|REPLACE} INTO t (SELECT ... FROM t ...);
Exception: The preceding prohibition does not apply if you are using a subquery for the modified table in the
FROM
clause. Example:
UPDATE t ... WHERE col = (SELECT (SELECT ... FROM t...) AS _t ...);
Here the prohibition does not apply because a subquery in the
FROM
clause is materialized as a temporary table, so the relevant rows in
t
have already been selected by the time the update to
t