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
   

Answer 2

It's incorrect, but you can try this instead:

select
    a.x,
    ( select b.y from b where b.v = a.v) as by,
    ( select b.z from b where b.v = a.v) as bz
from a

you can also use subquery in join

 select
        a.x,
        b.y,
        b.z
    from a
    left join (select y,z from b where ... ) b on b.v = a.v

or

   select
        a.x,
        b.y,
        b.z
    from a
    left join b on b.v = a.v

Answer 3

you can use cross apply:

select
    a.x,
    bb.y,
    bb.z
from
    a
    cross apply
    (   select b.y, b.z
        from b
        where b.v = a.v
    ) bb

If there will be no row from b to mach row from a then cross apply wont return row. If you need such a rows then use outer apply

If you need to find only one specific row for each of row from a, try:

    cross apply
    (   select top 1 b.y, b.z
        from b
        where b.v = a.v
        order by b.order
    ) bb

Answer 4

In Oracle query

select a.x
            ,(select b.y || ',' || b.z
                from   b
                where  b.v = a.v
                and    rownum = 1) as multple_columns
from   a

can be transformed to:

select a.x, b1.y, b1.z
from   a, b b1
where  b1.rowid = (
       select b.rowid
       from   b
       where  b.v = a.v
       and    rownum = 1
)

Is useful when we want to prevent duplication for table A. Similarly, we can increase the number of tables:

.... where (b1.rowid,c1.rowid) = (select b.rowid,c.rowid ....

Answer 5

View this web: http://www.w3resource.com/sql/subqueries/multiplee-row-column-subqueries.php

Use example

select ord_num, agent_code, ord_date, ord_amount  
from orders  
where(agent_code, ord_amount) IN  
(SELECT agent_code, MIN(ord_amount)  
FROM orders   
GROUP BY agent_code);    

Answer 6

Can't you use JOIN like this one?

SELECT
a.x , b.y, b.z 
FROM a 
LEFT OUTER JOIN b ON b.v = a.v

(I don't know Oracle Syntax. So I wrote SQL syntax)