Unanswered: How to determine, inside a function, if a linked-server-query returned results
Hi, have configured an ODBC linked server for an Adaptive Server Anywhere (ASA6.0) database.
I have to write a function (not a procedure) that receives a number (@Code) and returns 1 if it was found on a table in the linked server, or 0 if not. Looks very simple...
One problem, is that the queries on a linked-server must be made through the OPENQUERY statement, which doesen't support dynamic parameters. I've solved this making the whole query a string, and executing it, something like this:
SET @SQL='SELECT * FROM OPENQUERY(CAT_ASA, ''SELECT code FROM countries WHERE code=' + @Code + ''')'
EXEC sp_executesql @SQL
(CAT_ASA is the linked-server's name)
Then, i would use @@ROWCOUNT to determine if the code exists or not. But before this, a problem appears: sp_executesql is not allowed within a function (only extended procedures are allowed).
Does somebody know how to make what i want?? I prefer to avoid using temporary tables.
I never worked with an ASA6 db but how about using four-part naming instead of OpenQuery? In a normal query, you can use variables in your where clauses. So, if the column type of CODE is not something out of the ordinary and recognized by SQL Server, everything should run fine. There could be interface problems but usually with a query as simple as yours, it should work.
This is a simple solution that doesn't really answer your question. Consider it as a possible workaround.
Thanks for your answer, Skip. I also tried using a four part name, but SQL server gave me a message saying that the ODBC Interface doesnt support four-part names. I tried with a 3 part name (linkedservername.database.table), but it still doesnt works. The error was diferent (so, I supose that the names with this ODBC interface must have three parts). I read in another thread that the only way to make a query to a linked server was using OPENQUERY or OPENROWSET. Im not really sure about that, but i tried many ways using 3 or 4 part names and it never worked.
In addition i tried something like this:
SELECT * FROM OPENQUERY(CAT_ASA,'SELECT code FROM COUNTRIES') WHERE code=@Code
Here i dont have to use an EXEC, so it works in a function, and i can filter the results with a condition. The problem is (sorry for not saying it before) that i wrote a very simple example, but the real query has 4 nested joins, and (because of performance) i should make it in only 1 query.
Thats why I cannot make something like this:
SELECT * FROM OPENQUERY(CAT_ASA,'SELECT * FROM Table1')
INNER JOIN (OPENQUERY(CAT_ASA,'SELECT * FROM Table2') ON .... )
Because i would make 4 OPENQUERY, which results in a very poor performance (10/14 secs per query!!!).
Another solution would be making the join inside the OPENQUERY, and filtering the results in SQL Server, like this:
SELECT * FROM OPENQUERY(CAT_ASA,'SELECT * FROM Table1 inner join (Table2 inner join (Table3 inner join Table 4 on...) on....).....
Obviously this is worse than using 4 openquerys, because four joins without conditions (except on PKs) would return a very big quantity of records (in the order of 6.000.000.000!!!!!) and, after the conditions, that number would be reduced to 0 or 1 record (remember, i must check only the EXISTENCE of a record). That would be very inefficient.
So, I think in two ways for solving this:
1) Using the right part names (3 or 4), and making a normal query.
2) Find another method to execute a string query (or, more precisely, to determine if a string query has results), that can be used inside a function.