Self-join of a subquery
Yes, just alias the queries:
SELECT *
FROM (
SELECT *
FROM table
) t1
JOIN (
SELECT *
FROM table
) t2
ON t1.column < t2.other_column
Do you mean, the result of a query on a table, to that same table. If so, then Yes, it's possible... e.g.
--Bit of a contrived example but...
SELECT *
FROM Table
INNER JOIN
(
SELECT
UserID, Max(Login) as LastLogin
FROM
Table
WHERE
UserGroup = 'SomeGroup'
GROUP BY
UserID
) foo
ON Table.UserID = Foo.UserID AND Table.Login = Foo.LastLogin
You can do so with WITH:
WITH subquery AS(
SELECT * FROM TheTable
)
SELECT *
FROM subquery q1
JOIN subquery q2 on ...
Or by creating a VIEW that contains the query, and joining on that:
SELECT *
FROM TheView v1
JOIN TheView v2 on ...
Or the brute force approach: type the subquery twice:
SELECT *
FROM (
SELECT * FROM TheTable
) sub1
LEFT JOIN (
SELECT * FROM TheTable
) sub2 ON ...