Avoid multiple rows in join - sql

Question

Suppose that I have three tables, A, B and C:
Table A:
C1 C2 Dt
-------------
1 2 8 pm
1 2 10 pm
Table B:
C1 C2 Ind
-------------
1 2 123
1 2 456
Table C:
C1 C2 C3 C4 Ind
-------------------
1 2 a b 123
1 2 c d 123
1 2 e f 123
1 2 g h 456
As you can see, table B and C have a matching index, while A doesn't. How can I join the three tables so that the first row of A (ordered by the 'dt' column) will only match the rows in C which index is the first in B (ordered by Ind)? The same would apply for the other rows.
What I have tried is to create a simple join:
SELECT *
FROM A JOIN B
ON A.C1 = B.C1
AND A.C2 = B.C2
JOIN C ON A.C1 = C.C1
AND A.C2 = C.C2
AND B.IND = C.IND
I know this doesn't work, because each row in A will match all the rows in B and then match all the rows in C. In other words, there is no unique match.
Another approach I have thought made use of two selects:
SELECT *
FROM B JOIN (
SELECT C1, C2, C3, C4, Ind,
row_number() OVER (PARTITION BY C1, C2, ind ORDER BY C1, C2, ind) AS num_row
FROM C
) table_c
ON B.IND = table_c.IND
AND B.C1 = table_c.C1
AND B.C2 = table_c.C2
JOIN (
SELECT C1, C2, DT, row_number() OVER (ORDER BY DT) AS num_row
FROM A
) table_a
ON table_a.num_row = table_c.num_row
AND table_a.C1 = table_c.C1
AND table_a.C2 = table_c.C2
But those tables are very big and every approach that I have tried, would use multiple selects and is very slow. So I was wondering what would be the best way to do this.

Answer 1

Tables A and B have a one to one relationship. So joining them on a unique id based on the order of each should solve the first part of the problem.
create table newA as select rownum as uniq_id, A.* from A order by dt;
create table newB as select rownum as uniq_id, B.* from B order by ind;
select * from newA inner join newB on newA.uniq_id = newB.uniq_id;
Then with your new query, join on C.
select *
from
C
inner join (select
newB.Ind as ind
from
newA
inner join newB on newA.uniq_id = newB.uniq_id)
as sub on C.ind = sub.ind
I'm sure this could be done with temp tables or strictly in sql but that will depend on your implementation

Answer 2

You can use ROW_NUMBER effectively here
WITH arn
AS (SELECT a.c1,
a.c2,
"Dt",
Row_number()
over (
PARTITION BY a.c1, a.c2
ORDER BY "Dt")rn
FROM a),
brn
AS (SELECT b.c1,
b.c2,
b."Ind",
Row_number()
over (
PARTITION BY b.c1, b.c2
ORDER BY b."Ind") rn
FROM b)
SELECT *
FROM arn a
inner join brn b
ON a.c1 = b.c1
AND a.c2 = b.c2
AND a.rn = b.rn
Inner join c
ON b.c1 = c.c1
AND b.c2 = c.c2
AND b."Ind" = c."Ind"
Demo