在SELECT语句中指定列名作为参数？

Question

I need to do something like this, but it always fails with 'Error converting data type varchar to int':

DECLARE @intParam INT
DECLARE @ColName VARCHAR(64)

SET @ColName='intcolumn'

SET @intParam = SELECT @ColName FROM myTable

How do I accomplish something like this? I can see the problem is that the SELECT statement simply returns the column name as a string, but I am not sure how to fix that. I am using SQL Server 2008R2.

Answer 1

You need to use dynamic sql:

• build your dynamic SQL query (take a look at @SQL variable in sample below)
• use output parameter to get value back from dynamic sql (take a look at @intParam and @intParam_out in sample below)
• execute dynamic sql using sp_executesql

DECLARE @intParam INT
DECLARE @ColName VARCHAR(64)

SET @ColName='intcolumn'

DECLARE @SQL NVARCHAR(1000)
SET @SQL = 'SELECT @intParam_out = ' + @ColName + ' FROM myTable'
exec sp_executesql @SQL, N'@intParam_out int OUTPUT', @intParam_out = @intParam OUTPUT

Answer 2

使用Cast ：

SET @intParam = SELECT cast(@ColName as int) FROM myTable