I would like to do something like
(SELECT ... FROM ...) AS my_select
WHERE id IN (SELECT MAX(id) FROM my_select GROUP BY name)
Is it possible to somehow do the "AS my_select" part (i.e. assign an alias to a SELECT statement)?
(Note: This is a theoretical question. I realize that I can do it without assign an alias to a SELECT statement, but I would like to know whether I can do it with that.)
Not sure exactly what you try to denote with that syntax, but in almost all RDBMS-es you can use a subquery in the FROM clause (sometimes called an "inline-view"):
SELECT..
FROM (
SELECT ...
FROM ...
) my_select
WHERE ...
In advanced "enterprise" RDBMS-es (like oracle, SQL Server, postgresql) you can use common table expressions which allows you to refer to a query by name and reuse it even multiple times:
-- Define the CTE expression name and column list.
WITH Sales_CTE (SalesPersonID, SalesOrderID, SalesYear)
AS
-- Define the CTE query.
(
SELECT SalesPersonID, SalesOrderID, YEAR(OrderDate) AS SalesYear
FROM Sales.SalesOrderHeader
WHERE SalesPersonID IS NOT NULL
)
-- Define the outer query referencing the CTE name.
SELECT SalesPersonID, COUNT(SalesOrderID) AS TotalSales, SalesYear
FROM Sales_CTE
GROUP BY SalesYear, SalesPersonID
ORDER BY SalesPersonID, SalesYear;
(example from http://msdn.microsoft.com/en-us/library/ms190766(v=sql.105).aspx)
You can do this using the WITH clause of the SELECT statement:
;
WITH my_select As (SELECT ... FROM ...)
SELECT * FROM foo
WHERE id IN (SELECT MAX(id) FROM my_select GROUP BY name)
That's the ANSI/ISO SQL Syntax. I know that SQL Server, Oracle and DB2 support it. Not sure about the others...
Yes, but you can select only one column in your subselect
SELECT (SELECT id FROM bla) AS my_select FROM bla2
You could store this into a temporary table.
So instead of doing the CTE/sub query you would use a temp table.
Good article on these here http://codingsight.com/introduction-to-temporary-tables-in-sql-server/
