Error while linked server is used to verify the existence of a table

Question

Hi All,
Pls help me solve an issue related to linked Server..
Following is my query:
IF EXISTS (select 1 from [LinkedServerName].Sales.sys.tables where name = 'SalesTable') 
BEGIN
 DECLARE @LastSales varchar(25) 
 SET @LastSales = (select CONVERT(VARCHAR(25),max(LastSalesTime)) from [LinkedServerName].SalesDB.dbo.SalesTable)
END
What should happen is, it should check the existence of SalesTable on Linked Server (select 1 from [LinkedServer].Sales.sys.tables where name = 'SalesTable'), and only after the it returns 1, the variable @LastSales should be alloted a value.
But in my case, as soon as I run the code, it gives the error:
The OLE DB provider "SQLNCLI10" for linked server "LinkedServerName" does not contain the table ""Sales"."dbo"."SalesTable"". 
The table either does not exist or the current user does not have permissions on that table.
My question is that if the condition fails at the very outset returning null (as the table does not exist), then why it is entering BEGIN and throwing the error.
All your valuable inputs are appreciated !!

Answer 1

Inconsistency is the hailmark of SQL Server.
If you say:
IF EXISTS (select 1 from Sales.sys.tables where name = 'SalesTable') 
BEGIN
 DECLARE @LastSales varchar(25) 
 SET @LastSales = (select CONVERT(VARCHAR(25),max(LastSalesTime)) from        SalesDB.dbo.SalesTable)
END
This will work as you expect. That is, if the table does not exist, the batch will parse and produce no result. This is because SQL Server has deferred name resolution for tables. If a table is missing at compile time, SQL Server suppresses the error in
hope that the table will be there at run-time.
But there is an exception to this. For table sources on remote data sources, there is no deferred name resolution, but the table has to be there at compile time. This is quite ironic. Personally, I think deferred name resolution (which was introduced in
SQL 7) is a big misfeature, but I could buy if there was deferred name resolution for objects on linked server, since the server may be down, and you have coded for this like you have above. Well, if the server is down, the IF EXISTS will fail to compile to.
You will need to introduce a new scope somewhere to avoid the problem. For instance:
IF EXISTS (select 1 from [LinkedServerName].Sales.sys.tables where name = 'SalesTable') 
BEGIN
   DECLARE @LastSales varchar(25) 
   EXEC [Linkedservername].SalesDB.sys.sp_executesql
        N'SET @LastSales = (select CONVERT(VARCHAR(25),max(LastSalesTime)) from SalesTable)',
        N'@LastSales varchar(25) OUTPUT', @LastSales
END
Erland Sommarskog, SQL Server MVP, [email protected]