前言

一些小技巧，可以帮助我们解决很多麻烦的事情。

更新自身表

UPDATE `table_a` SET `table_a`.`key` = ‘name’ WHERE `table_a`.`key` IN (SELECT b.`key` FROM `table_a` AS a JOIN `table_b` AS b ON a.`key` = b.`key`);

然而，MySQL并不支持，所以可以换另外一种。

UPDATE `table_a` AS a JOIN (SELECT b.`key` FROM `table_a` AS a JOIN `table_b` AS b ON a.`key` = b.`key`) AS b ON a.`key` = b.`key` SET a.`key` = ‘name’;

优化子查询：

使用JOIN语句来优化。

使用聚合查询

暂无好的想法~

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本文转载自IMJCW

原文链接：JOIN使用技巧