联接与子查询 [英] Join vs. sub-query

问题描述

我是一个老式的MySQL用户，并且总是优先使用JOIN而不是子查询.但是如今，每个人都使用子查询，而我讨厌它.我不知道为什么

I am an old-school MySQL user and have always preferred JOIN over sub-query. But nowadays everyone uses sub-query, and I hate it; I don't know why.

我缺乏理论判断力来判断自己是否有差异.子查询是否与JOIN一样好，因此不必担心吗?

I lack the theoretical knowledge to judge for myself if there is any difference. Is a sub-query as good as a JOIN and therefore is there nothing to worry about?

推荐答案

来自MySQL手册(

左[OUTER] JOIN可能比同等子查询更快，因为服务器可能能够更好地对其进行优化-这不仅限于MySQL Server.

A LEFT [OUTER] JOIN can be faster than an equivalent subquery because the server might be able to optimize it better—a fact that is not specific to MySQL Server alone.

因此子查询的速度可能比LEFT [OUTER] JOIN慢，但我认为它们的优势是可读性稍高.

So subqueries can be slower than LEFT [OUTER] JOIN, but in my opinion their strength is slightly higher readability.

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