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How do I write a series of SQL Server SELECT statements that compare tables in two databases with variables for the db names?

Posted on 2014-12-30
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Last Modified: 2014-12-30
I want to write something like this

declare @db1 nvarchar(100);
declare @db2 nvarchar(100);

select id from [@db1]..MyTable t1 INNER JOIN [@db2]..MyTable t2 on [t1].id=[t2].id

but clearly SQL Server doesn't like the database names in variables - how can I achieve what I am trying to do?

I'm on but I'd like it as generic as possible for versions:
Microsoft SQL Server 2012 - 11.0.5058.0 (X64)
      May 14 2014 18:34:29
      Copyright (c) Microsoft Corporation
      Standard Edition (64-bit) on Windows NT 6.3 <X64> (Build 9600: )
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Question by:purplesoup
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Accepted Solution

by:
Vikas Garg earned 2000 total points
ID: 40523450
Hi,

You can do something like this
declare @db1 nvarchar(100) = 'KPIFStaging'
declare @db2 nvarchar(100) = 'WintimeStaging'
DECLARE @SQL NVARCHAR(500)


SET @SQL = 'SELECT * FROM ' + @db1 + '.[dbo].[TransactionAudit]'

--PRINT @SQL -- To check the SQL

EXECUTE(@SQL)

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Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 40523459
I concur you cannot do without going dynamic sql  ( or going ad-hoc sql from outside the sql as such)
you cannot use variables for any of the following : database, table, column names etc ...
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Author Comment

by:purplesoup
ID: 40523492
Ok thanks - when I saw the answer I guessed there wasn't going to be some more useful way to do it. I'm supplying a script to someone and it would have been useful for them to just set the names of the databases at the top of the script, but I think I'm just going to tell them to do a find and replace on the database names, going the dynamic sql route is going to ruin readability.
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