Referencing column from WITH-Subselect

Question

The problem is as following: I'm using a subquery and I need to join

WITH subselect_from_A AS (
    SELECT A.A_ID FROM A
)
SELECT B.D_ID FROM B, subselect_from_A WHERE B.B_ID = 
A.A_ID
/* or instead: subselect_from_A.A_ID */

;

How Do I reference the column form the subselect?

Answer 1

First of all, you should stop using deprecated implicit joins and use explicit joins instead. Then you can use table aliases for this:

WITH subselect_from_A AS (
    SELECT A.A_ID FROM A --doesn't really seem like a sub-select
)
SELECT B.D_ID, A.A_ID
FROM B
INNER JOIN subselect_from_A AS A
    ON B.B_ID = A.A_ID;

Answer 2

Same way you would with a regular table.

WITH subselect_from_A AS (
    SELECT A.A_ID FROM A
)
SELECT B.D_ID, subselect_from_A.A_ID FROM B, subselect_from_A
WHERE B.B_ID = subselect_from_A.A_ID;