How to set value to variable using 'execute' in t-sql?

Question

DECLARE @dbName nvarchar(128) = 'myDb'
DECLARE @siteId int 
exec ('SELECT TOP 1 @siteId = Id FROM ' + @dbName + '..myTbl')  
select @siteId

When I run the script above I get the following error

Msg 137, Level 15, State 1, Line 1
Must declare the scalar variable "@siteId".

(1 row(s) affected)

Why and how to fix it?

Thank you

Answer 1

You can use output parameters with sp_executesql.

DECLARE @dbName nvarchar(128) = 'myDb'
DECLARE @siteId int 
DECLARE @SQL nvarchar(max) = N'SELECT TOP 1 @outputFromExec = Id FROM ' + quotename(@dbName) + N'..myTbl'
exec sp_executesql @SQL, N'@outputFromExec int out', @siteId out
select @siteId