Is there any SQL subquery syntax that lets you define, literally, a temporary table?
For example, something like
SELECT MAX(count) AS max, COUNT(*) AS count FROM ( (1 AS id, 7 AS count), (2, 6), (3, 13), (4, 12), (5, 9) ) AS mytable INNER JOIN someothertable ON someothertable.id=mytable.id
This would save having to do two or three queries: creating temporary table, putting data in it, then using it in a join.
I am using MySQL but would be interested in other databases that could do something like that.
I suppose you could do a subquery with several
SELECTs combined with
SELECT a, b, c, d FROM ( SELECT 1 AS a, 2 AS b, 3 AS c, 4 AS d UNION ALL SELECT 5 , 6, 7, 8 ) AS temp;
You can do it in PostgreSQL:
=> select * from (values (1,7), (2,6), (3,13), (4,12), (5,9) ) x(id, count); id | count ----+------- 1 | 7 2 | 6 3 | 13 4 | 12 5 | 9
In standard SQL (SQL 2003 – see http://savage.net.au/SQL/) you can use:
INSERT INTO SomeTable(Id, Count) VALUES (1, 7), (2, 6), (3, 13), ...
With a bit more chasing, you can also use:
SELECT * FROM TABLE(VALUES (1,7), (2, 6), (3, 13), ...) AS SomeTable(Id, Count)
Whether these work in MySQL is a separate issue – but you can always ask to get it added, or add it yourself (that’s the beauty of Open Source).
In Microsoft T-SQL 2008 the format is:
SELECT a, b FROM (VALUES (1, 2), (3, 4), (5, 6), (7, 8), (9, 10) ) AS MyTable(a, b)
I.e. as Jonathan mentioned above, but without the ‘table’ keyword.
I found this link Temporary Tables With MySQL
CREATE TEMPORARY TABLE TempTable ( ID int, Name char(100) ) TYPE=HEAP; INSERT INTO TempTable VALUES( 1, "Foo bar" ); SELECT * FROM TempTable; DROP TABLE TempTable;
CREATE TEMPORARY TABLE ( ID int, Name char(100) ) SELECT ….
Read more at : http://dev.mysql.com/doc/refman/5.0/en/create-table.html
( near the bottom )
This has the advantage that if there is any problem populating the table ( data type mismatch ) the table is automatically dropped.
An early answer used a FROM SELECT clause. If possible use that because it saves the headache of cleaning up the table.
Disadvantage ( which may not matter ) with the FROM SELECT is how large is the data set created. A temporary table allows for indexing which may be critical. For the subsequent query. Seems counter-intuitive but even with a medium size data set ( ~1000 rows), it can be faster to have a index created for the query to operate on.
In a word, yes. Even better IMO if your SQL product supports common table expressions (CTEs) i.e. easier on the eye than using a subquery plus the same CTE can be used multiple times e.g. this to ‘create’ a sequence table of unique integers between 0 and 999 in SQL Server 2005 and above:
WITH Digits (nbr) AS ( SELECT 0 AS nbr UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9 ), Sequence (seq) AS ( SELECT Units.nbr + Tens.nbr + Hundreds.nbr FROM Digits AS Units CROSS JOIN Digits AS Tens CROSS JOIN Digits AS Hundreds ) SELECT S1.seq FROM Sequence AS S1;
except you’d actually do something useful with the Sequence table e.g. parse the characters from a VARCHAR column in a base table.
HOWEVER, if you are using this table, which consists only of literal values, multiple time or in multiple queries then why not make it a base table in the first place? Every database I use has a Sequence table of integers (usually 100K rows) because it is so useful generally.