Creating Stored Procedure in Local DB Referencing Linked Server Tables

linked-serversql serverstored-procedures

I currently have a local server linked to a remote server.

Is it possible to create a stored procedure within the local server, but querying data from tables within the linked server. I am aware there may be performance issues, but I am reluctant to create the sp on the linked server as it would require obtaining permissions to do so.

I believe my problem is syntax but I cannot identify exactly what,

USE [LOCALDB]  --my local database or should I reference linked server db here
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE PROC [dbo].[mystoredprocedure]
    DECLARE @linkedserv NVARCHAR(150)
    DECLARE @linkeddb NVARCHAR(150)

    SET @linkedserv = 'HOSTNAME\SERVER';
    SET @linkeddb = 'remotedb';

    SELECT (CASE LTRIM(RTRIM([COLUMN1]))
        WHEN '' Then ''
        WHEN 'THIS' THEN 'THAT'
        WHEN 'NOW' THEN 'NEVER'
        ELSE 'OTHER' END) [Options]
    INTO #TempTable
    FROM @linkedserv.@linkeddb.dbo.TableOnLinkedServer --is this an issue?
    FULL OUTER JOIN OtherTableOnLinkedServer ON TableOnLinkedServer.COUMN1 = 
    OtherTableOnLinkedServer.COLUMN0

The linked servers db and it's tables are queried multiple times throughout the sp so finding a shorthand way of referencing them would be great,

Cheers

Best Answer

You can't parameterize entity names into a T-SQL statement. In order to do this you need to (a) create the #temp table first, and (b) use dynamic SQL. Here is one approach:

CREATE PROCEDURE [dbo].[mystoredprocedure]
AS
BEGIN
  SET NOCOUNT ON;

  DECLARE @exec nvarchar(256),
    @linkedserv nvarchar(150),
    @linkeddb   nvarchar(150),
    @sql        nvarchar(max);

  SELECT @linkedserv = N'HOSTNAME\SERVER',
         @linkeddb   = N'remotedb';

  SELECT @exec = QUOTENAME(@linkedserv) + N'.'
               + QUOTENAME(@linkeddb) + N'.sys.sp_executesql';

  CREATE TABLE #TempTable([Options] varchar(64));

  SELECT @sql = N'SELECT (CASE LTRIM(RTRIM(ot.[COLUMN1]))
        WHEN ''''     THEN ''''
        WHEN ''THIS'' THEN ''THAT''
        WHEN ''NOW''  THEN ''NEVER''
        ELSE ''OTHER'' END) AS [Options]
    FROM dbo.TableOnLinkedServer AS t
    FULL OUTER JOIN dbo.OtherTableOnLinkedServer AS ot
      ON t.COLUMN1 = ot.COLUMN0;';

  INSERT #TempTable([Options]) EXEC @exec @sql;   

  SELECT * FROM #TempTable;
END
GO

You could do it all inside dynamic SQL, so if knowing the columns up front is a challenge, there is a way. But it's messy, assuming you actually need a #temp table, because then everything you do with #TempTable has to be done inside the dynamic SQL.

CREATE PROCEDURE [dbo].[mystoredprocedure]
AS
BEGIN
  SET NOCOUNT ON;

  DECLARE @exec nvarchar(256),
    @linkedserv nvarchar(150),
    @linkeddb   nvarchar(150),
    @sql        nvarchar(max);

  SELECT @linkedserv = N'HOSTNAME\SERVER',
         @linkeddb   = N'remotedb';

  SELECT @exec = QUOTENAME(@linkedserv) + N'.'
               + QUOTENAME(@linkeddb) + N'.sys.sp_executesql';

  SELECT @sql = N'SELECT (CASE LTRIM(RTRIM(ot.[COLUMN1]))
        WHEN ''''     THEN ''''
        WHEN ''THIS'' THEN ''THAT''
        WHEN ''NOW''  THEN ''NEVER''
        ELSE ''OTHER'' END) AS [Options]
    INTO #TempTable
    FROM dbo.TableOnLinkedServer AS t
    FULL OUTER JOIN dbo.OtherTableOnLinkedServer AS ot
      ON t.COLUMN1 = ot.COLUMN0;

  SELECT * FROM #TempTable;';

  EXEC @exec @sql;   
END
GO

Please look at the obligatory Erland Sommarskog article on dynamic T-SQL to ensure you don't end up creating an embarrassing SQL Injection vulnerability.

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