测试MySQL表中是否存在行的最佳方法 [英] Best way to test if a row exists in a MySQL table

问题描述

我试图找出表中是否存在一行.使用MySQL，最好执行如下查询:

I'm trying to find out if a row exists in a table. Using MySQL, is it better to do a query like this:

SELECT COUNT(*) AS total FROM table1 WHERE ...

并检查总数是否为非零或执行以下查询是否更好:

and check to see if the total is non-zero or is it better to do a query like this:

SELECT * FROM table1 WHERE ... LIMIT 1

并检查是否返回了任何行?

and check to see if any rows were returned?

在两个查询中，WHERE子句均使用索引.

In both queries, the WHERE clause uses an index.

推荐答案

您也可以尝试EXISTS:

SELECT EXISTS(SELECT * FROM table1 WHERE ...)

，并按照文档，您可以SELECT任何内容.

and per the documentation, you can SELECT anything.

传统上，EXISTS子查询以SELECT *开头，但是它可以 以SELECT 5或SELECT column1或其他任何内容开头. MySQL 忽略此类子查询中的SELECT列表，因此没有区别.

Traditionally, an EXISTS subquery starts with SELECT *, but it could begin with SELECT 5 or SELECT column1 or anything at all. MySQL ignores the SELECT list in such a subquery, so it makes no difference.

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