Subquery in select - non-grouped values in 'IN' clause - sql

Question

Assume the following simplified schema:
create table main_table
(
a number,
b number,
c number
);
create table other_table
(
c number,
d number
)
Now, what i want to achieve:
I have a query on main_table, that groups by a,b.
I need to use the "all values of c" in subquery in select clause to get some data from other tables.
I can't join to the other table unfortunately.
Pseudocode would be:
select mt.a,
mt.b,
(select /* some aggregated value */
from other_table ot
where ot.c in (all_values_of_c_within_group)
)
from main table mt
group by mt.a, mt.b
There are two ways i know it's possible to handle this:
Use join on other_table and then aggregate values from there - unfortunately i can't do it, because of how the real query is structured (3 nested views, 800 sloc, 30 values in group by - long story)
Use listagg and then 'delistagg' it with 'instr'. Pseudocode:
/*(...)*/
(select /* some_aggregated_value */
from other_table ot
where instr(',' || listagg(
to_char(mt.c), ',') within group (order by 1),
',' || ot.c) > 0
)
/*(...)*/
But that's just terrible code, and it automatically prevents using any potentially existing indexes on other_table.c.
Is there a syntax to properly get "all values of column within group?

Answer 1

It is unclear without some data and expected results what you are trying to achieve but I think you do what you want using collections:
SQL Fiddle
Oracle 11g R2 Schema Setup:
create table main_table( a, b, c ) AS
SELECT 1, 1, 1 FROM DUAL UNION ALL
SELECT 1, 1, 2 FROM DUAL UNION ALL
SELECT 1, 1, 3 FROM DUAL
/
create table other_table( c, d ) AS
SELECT 1, 4 FROM DUAL UNION ALL
SELECT 3, 6 FROM DUAL UNION ALL
SELECT 5, 8 FROM DUAL
/
CREATE TYPE number_table AS TABLE OF NUMBER
/
Query 1:
SELECT a,
b,
( SELECT LISTAGG( d, ',' ) WITHIN GROUP ( ORDER BY d )
FROM other_table
WHERE c MEMBER OF m.cs
) ds
FROM (
SELECT a,
b,
CAST( COLLECT( c ) AS number_table ) AS cs
FROM main_table
GROUP BY a, b
) m
Results:
| A | B | DS |
|---|---|-----|
| 1 | 1 | 4,6 |
Query 2: But it seems simpler to just use a LEFT OUTER JOIN:
SELECT a,
b,
LISTAGG( d, ',' ) WITHIN GROUP ( ORDER BY d ) ds
FROM main_table m
LEFT OUTER JOIN other_table o
ON ( m.c = o.c )
GROUP BY a, b
Results:
| A | B | DS |
|---|---|-----|
| 1 | 1 | 4,6 |

Answer 2

You may just be able to aggregate the subquery, e.g. with sum as the aggregate function:
select mt.a,
mt.b,
sum(
(select d
from other_table ot
where ot.c = mt.c)
) as sum_d
from main_table mt
group by mt.a, mt.b;
With some made-up data:
insert into main_table values (1, 2, 3);
insert into main_table values (1, 2, 4);
insert into main_table values (2, 3, 4);
insert into main_table values (2, 3, 5);
insert into main_table values (2, 3, 6);
insert into other_table values (3, 10);
insert into other_table values (4, 11);
insert into other_table values (5, 12);
insert into other_table values (6, 13);
that query gives:
A B SUM_D
---------- ---------- ----------
2 3 36
1 2 21
As you noted, with an extra row:
insert into main_table values (2, 3, 4);
that query counts a matching c's d value multiple times, so you get 47 instead of 36:
A B SUM_D
---------- ---------- ----------
2 3 47
1 2 21
You can add a distinct:
select mt.a,
mt.b,
sum(distinct
(select d
from other_table ot
where ot.c = mt.c)
) as sum_d
from main_table mt
group by mt.a, mt.b;
A B SUM_D
---------- ---------- ----------
1 2 21
2 3 36
This assumes that c, or at least the combination of c, d, is unique in other_table.

Answer 3

This should work, and should not impose the uniqueness requirements on other_table that Alex's answer does.
select mt.a,
mt.b,
(select sum(d) /* some aggregated value */
from other_table ot
where ot.c in ( SELECT mt2.c
FROM main_table mt2
WHERE mt2.a = mt.a AND mt2.b = mt.b
)
) agg
from main_table mt
group by mt.a, mt.b;
It has to go to main_table again for each group, but considering you already are accessing those records, we should be talking about extra logical I/O instead of extra physical I/O.
Using Alex Poole's test data (with the duplicate MAIN_TABLE row), I get this in 12c:
+---+---+-----+
| A | B | AGG |
+---+---+-----+
| 2 | 3 | 36 |
| 1 | 2 | 21 |
+---+---+-----+