MySQL-AND条件 [英] MySQL - AND condition

问题描述

假设我有这样的查询:

SELECT bla WHERE foo LIKE '%bar%' AND boo = 'bar' AND whatvr IN ('foo', 'bar')...

我想知道MySQL在检索结果时是否继续检查所有条件. 例如.如果foo不是LIKE %bar%，它将继续检查是否boo = 'bar'，依此类推吗?

I was wondering if MySQL continues to check all conditions when retrieving results. For eg. if foo is not LIKE %bar%, will it continue to check if boo = 'bar', and so on ?

如果我最后放置不太可能成立的条件会更快吗?

Would it be any faster if I put conditions that are less likely to be true at the end?

很抱歉，如果这似乎是一个愚蠢的问题，那么对于SQL来说，我是一个完全菜鸟:)

I'm sorry if this seems to be stupid question, I'm a complete noob when it comes to SQL :)

推荐答案

我认为无法保证是否会短路多个条件，但是...

I don't think there are any guarantees about whether or not multiple conditions will be short-circuited, but...

通常，您应该将查询优化器视为黑匣子，并假设-除非有相反的证据，否则它会正确执行其工作.优化者的工作是确保尽可能高效地检索所请求的数据.如果最有效的计划涉及短路，那就去做；如果没有，那就不会.

In general, you should treat the query optimiser as a black box and assume -- unless you have evidence to the contrary -- that it will do its job properly. The optimiser's job is to ensure that the requested data is retrieved as efficiently as possible. If the most efficient plan involves short-circuiting then it'll do it; if it doesn't then it won't.

(当然，查询优化器并不完美.如果您有证据表明查询没有以最佳方式执行，那么通常值得重新排序和/或重新定义查询以查看是否有任何更改.)

(Of course, query optimisers aren't perfect. If you have evidence that a query isn't being executed optimally then it's often worth re-ordering and/or re-stating the query to see if anything changes.)

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