SQL“如果存在..."动态查询 [英] SQL "if exists..." dynamic query

问题描述

假设我有一个存储在这样的变量中的查询(它实际上是动态填充的，并且更复杂，但这是出于演示目的):

Suppose I have a query stored in a variable like this (it's actually dynamically populated and more complex, but this is for demonstration purposes):

DECLARE @Query VARCHAR(1000) = 'SELECT * FROM dbo.MyTable'

是否可以检查查询是否返回任何结果?像这样的东西，但这是行不通的:

Is there a way to check if the query would return any results? Something like this, but this doesn't work:

IF EXISTS (@Query)
BEGIN
    -- do something
END

我想到的唯一方法是将结果放入临时表中，然后从中进行查询，但这并不理想，因为动态查询中的列可以变化，而且我真的不需要除了检查是否会返回某些行外，temp表完全出于任何原因.有更好的方法吗?

The only way that I can think of to do this is to put the results in a temp table and then query from that, but that is not ideal because the columns in the dynamic query can vary and I really don't need the temp table at all for any reason other than checking whether some rows would be returned. Is there a better way?

推荐答案

尝试执行动态查询并使用 @@ RowCount 查找行的存在.

Try Executing the Dynamic query and use @@RowCount to find the existence of rows.

DECLARE @Query  NVARCHAR(1000) = 'SELECT * FROM [dbo].[Mytable]',
        @rowcnt INT

EXEC Sp_executesql @query

SELECT @rowcnt = @@ROWCOUNT

IF @rowcnt > 0
  BEGIN
      PRINT 'row present'
  END 

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