IF EXISTS (SELECT 1 ...) vs IF EXITS (SELECT TOP 1 1 ...) [英] IF EXISTS (SELECT 1...) vs IF EXITS (SELECT TOP 1 1...)
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问题描述
这是一个纯粹的学术问题.这两个陈述实际上是否相同?
This is a purely academic question. Are these 2 statements effectively identical?
IF EXISTS (SELECT TOP 1 1 FROM Table1)
SELECT 1
ELSE
SELECT 0
对比
IF EXISTS (SELECT 1 FROM Table1)
SELECT 1
ELSE
SELECT 0
推荐答案
如果您查看这些查询的执行计划，您会发现它们是相同的.良好的编码实践会要求您忽略TOP 1"，但它们应该以任何一种方式运行.
If you view the execution plan for these queries you can see that they are identical. Good coding practices would ask that you leave out the "TOP 1" but they should run identical either way.
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