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摘要： 问题：mysql 对子查询的优化好像做的不好，比如最近在项目中用到一条查询语句：SELECT a.object_id,a.object_content FROM NEWS_PERSON_OBJECT a WHERE object_id in ( SELECT object_id FROM IMPORTANT_OBJECT_REL where object_type = 0 AND important_id=4);非常的耗时。 然而SELECT object_id FROM IMPORTANT_OBJECT_REL where object_type = 0 AND important_id.. 阅读全文