Is it possible to get multiple values from a subquery?

Question

Is there any way to have a subquery return multiple columns in oracle db? (I know this specific sql will result in an error, but it sums up what I want pretty well)

Answer 1

Here are two methods to get more than 1 column in a scalar subquery (or inline subquery) and querying the lookup table only once. This is a bit convoluted but can be the very efficient in some special cases.

1. You can use concatenation to get several columns at once:

   SELECT x, 
          regexp_substr(yz, '[^^]+', 1, 1) y,
          regexp_substr(yz, '[^^]+', 1, 2) z
     FROM (SELECT a.x,
                  (SELECT b.y || '^' || b.z yz
                     FROM b
                    WHERE b.v = a.v)
                     yz
             FROM a)
   

   You would need to make sure that no column in the list contain the separator character.

2. You could also use SQL objects:

   CREATE OR REPLACE TYPE b_obj AS OBJECT (y number, z number);
   
   SELECT x, 
          v.yz.y y,
          v.yz.z z
     FROM (SELECT a.x,
                  (SELECT b_obj(y, z) yz
                     FROM b
                    WHERE b.v = a.v)
                     yz
             FROM a) v