Is it possible to get multiple values from a subquery? - sql

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)
select
a.x,
( select b.y, b.z from b where b.v = a.v),
from a
I want a result like this:
a.x | b.y | b.z
---------------
1 | 2 | 3
I know it is possible to solve this problem through joins, but that is not what I am asking for.
My Question is simply if there is any way, to get two or more values out of a subquery? Maybe some workaround using dual? So that there is NO actual join, but a new subquery for each row?
EDIT: This is a principle question. You can solve all these problems using join, I know. You do not need subqueries like this at all (not even for one column). But they are there. So can I use them in that way or is it simply impossible?

Answer 1

A Subquery in the Select clause, as in your case, is also known as a Scalar Subquery, which means that it's a form of expression. Meaning that it can only return one value.
I'm afraid you can't return multiple columns from a single Scalar Subquery, no.
Here's more about Oracle Scalar Subqueries:
http://docs.oracle.com/cd/B19306_01/server.102/b14200/expressions010.htm#i1033549

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

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.
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.
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 4

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)

Answer 5

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 6

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 7

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);