SQL: WITH clause with parameters?

Question

In Oracle SQL Developer, I am using a WITH clause, in this (simplified) way:

WITH
foos AS
    SELECT *
    FROM my_table
    WHERE field = 'foo'
bars AS
    SELECT *
    FROM my_table
    WHERE field = 'bar'
SELECT *
FROM foo
INNER JOIN bar
ON foo.id = bar.id

I would like to be able to factor out the 'foo' and 'bar' strings, so that I can have something like:

WITH
subq(my_arg) AS
    SELECT *
    FROM my_table
    WHERE field = my_arg
SELECT *
FROM subq('foo')
INNER JOIN subq('bar')
ON subq('foo').id = subq('foo').id

Because, foos and bars are actually much bigger than this, and there are nut just two of them, so it is getting a bit hard to maintain.

I know this may be not possible with a WITH clause, but what would be the best solution to avoid writing this subquery multiple times? This may be actually quite simple, but I am quite new to SQL...

Thanks for your help.

Solution 1

You can reuse a WITH expression in the next one. But as far as I know you cannot parametrize it. So may be this could help:

WITH
foosAndbars AS 
    (SELECT *
     FROM [Very complex query] ).
foos AS (
    SELECT *
    FROM foosAndbars 
    WHERE field = 'foo'),
bars AS (
    SELECT *
    FROM foosAndbars 
    WHERE field = 'bar')
SELECT *
FROM foo
INNER JOIN bar
ON foo.id = bar.id

Solution 2

It seems this may be what you want:

SELECT *
FROM my_table foo
JOIN my_table bar ON foo.id = bar.id
JOIN my_table baz ON foo.id = baz.id
WHERE foo.field = 'foo'
AND bar.field = 'bar'
AND baz.field = 'baz'

If the WITH clause is doing a lot (and worth not repeating):

WITH cte AS SELECT * FROM mytable <with some complex SQL>
SELECT *
FROM cte foo
JOIN cte bar ON foo.id = bar.id
JOIN cte baz ON foo.id = baz.id
WHERE foo.field = 'foo'
AND bar.field = 'bar'
AND baz.field = 'baz'