TSQL verify sort order / UNION ALL

Question

CREATE PROCEDURE Test
AS
BEGIN
SELECT * FROM (
SELECT 1 AS a,'test1' as b, 'query1' as c
UNION ALL
SELECT 2 AS a,'test22' as b, 'query22' as c
UNION ALL
SELECT 2 AS a,'test2' as b, 'query2' as c
UNION ALL
SELECT 3 AS a,'test3' as b, 'query3' as c
UNION ALL
SELECT 4 AS a,'test4' as b, 'query4' as c
) As sample
FOR XML RAW
END
Can we guarantee that the stored procedure returns results in given order?
Normally it says when we insert these select query to temporary table we can't guarantee its inserting order. So we have to use order by clause. But most of time it gives same order. Can we enforce to give it some different order? Is this related with clustered
and non clustered indices.
In second case can we enforce inserting order by adding Identity column?
Explain more on behind logic as well. I'm checking whether I need to add ORDER BY in old Stored Procedures or not.

Answer 1

Can we guarantee that the stored procedure returns results in given order?  
No. The only way to get a guaranteed order is to use an ORDER BY clause.
Normally it says when we insert these select query to temporary table we can't guarantee its inserting order. So we have to use order by clause. But most of time it gives same order. Can we enforce to give it some different order? Is this related with
clustered and non clustered indices.  
The only way to get a guaranteed order is to use an ORDER BY clause. Anything else is happenstance.
In second case can we enforce inserting order by adding Identity column?   Explain more on behind logic as well. I'm checking whether I need to add ORDER BY in old Stored Procedures or not.
Again: the only way to get a guaranteed order is to use an ORDER BY clause.
Erland Sommarskog, SQL Server MVP, [email protected]