Question

In SQL Server 2008:

I have one table, and I want to do something along the following lines:

SELECT T1.stuff, T2.morestuff from
(
 SELECT code, date1, date2 from Table
) as T1
INNER JOIN
(
 SELECT code, date1, date2 from Table
) as T2

ON T1.code = T2.code and  T1.date1 = T2.date2

The two subqueries are exactly identical. Is there any way I can do this without repeating the subquery script?

Thanks

Karl

Answer 1

CTE:

;WITH YourQuery AS
(
 SELECT code, date1, date2 from Table
)
SELECT 
    T1.stuff, T2.morestuff 
    from YourQuery           T1
        INNER JOIN YourQuery T2 ON T1.code = T2.code and  T1.date1 = T2.date2

FYI

In the question, the code is using derived tables, also known as inline views. A subquery is a SELECT query that returns a single value and is nested inside a SELECT, INSERT, UPDATE, or DELETE statement, or inside another subquery. A subquery can be used anywhere an expression is allowed. See: http://msdn.microsoft.com/en-us/library/aa213252(SQL.80).aspx