Join three tables based on one key, putting data into same column - sql

Question

I have three tables that I am trying to join together to check that the proper data matches. I have table A which is a list of all accounts that a commission was paid on and what that commission amount was. I have Table B and Table C which are two tables that have commission calculations in it. The goal is to compare Table A to Table and to Table C and pulling back the amounts from both tables to ensure a match. The part I am struggling with is, Table A has all the accounts that are the base population. Table B has some and Table C as some. An account will be in either Table B or C, but never in both. I want to pull the payment from Table A, and then verify to the payment in Table B or C(whichever it occurs) and the same with commission. I then am doing a case when that compares the two fields and tells me if it matches are not.
+---------+---------+-----+------+
| Table A | | | |
+---------+---------+-----+------+
| Account | Uniq_ID | Pay | Comm |
| 12345 | ABCD | 100 | 10 |
| 23456 | OLPOL | 25 | 2 |
| 45678 | LKJHG | 200 | 15 |
| 96385 | LKJ67 | 250 | 26 |
+---------+---------+-----+------+
+---------+---------+-----+------+
| Table B | | | |
+---------+---------+-----+------+
| Account | Uniq_ID | Pay | Comm |
| 12345 | ABCD | 100 | 8 |
| 45678 | LKJHG | 200 | 15 |
+---------+---------+-----+------+
+---------+---------+-----+------+
| Table C | | | |
+---------+---------+-----+------+
| Account | Uniq_ID | Pay | Comm |
| 23456 | OLPOL | 25 | 2 |
| 96385 | LKJ67 | 250 | 32 |
+---------+---------+-----+------+
I am trying to get my results to show up in a columns called pay_ver and comm_verf, and it would populate with the data from either Table B or C based on which it matched with. I am hoping to have to output look like so....
+---------+---------+-----+----------+------+-----------+---------+
| Output | | | | | | |
+---------+---------+-----+----------+------+-----------+---------+
| Account | Uniq_ID | Pay | Pay_verf | comm | comm_Verf | Matched |
| 12345 | ABCD | 100 | 100 | 10 | 8 | No |
| 23456 | OLPOL | 25 | 25 | 2 | 2 | Yes |
| 45678 | LKJHG | 200 | 200 | 15 | 15 | Yes |
| 96385 | LKJ67 | 250 | 250 | 26 | 32 | No |
+---------+---------+-----+----------+------+-----------+---------+
This is the code I have used to join Table A to B, and Table A to C but I have done this in two separate queries giving me two outputs. I would like to be able to do this in one, so I only have one output.
select a.account, a.uniq_id, a.pay, b.pay as pay_verf, a.comm, b.comm as comm_verf,
CASE WHEN a.comm = b.comm THEN 'MATCHED'
ELSE 'UNMATCHED'
END as Matched
from tblA a
left join tblB b
on a.account = b.account
and a.uniq_id = b.uniq_id;
I can not just figure out how to also get it to join to Table C without adding an extra column.

Answer 1

You can do:
select
account, uniq_id, pay,
pay_total as pay_verf,
comm,
comm - comm_total as comm_verf,
case when comm = comm_total then 'Yes' else 'No' end as matched
from (
select
a.account, a.uniq_id, a.pay, a.comm,
coalesce(b.pay, 0) + coalesce(c.pay, 0) as pay_total,
coalesce(b.comm, 0) + coalesce(c.comm, 0) as comm_total
from table_a a
left join table_b b on a.account = b.account
left join table_c c on a.account = c.account
) x

Answer 2

You are very close. Just need to add one more join and an addition WHEN to your case statement. This should act like an if elseif else logic. So it checks if a.comm = b.comm and then checks a.comm = c.comm. If neither match if will set to unmatched. This works well because you stated the ID can't be in both B and C.
select a.account, a.uniq_id, a.pay, b.pay as pay_verf, a.comm, b.comm as comm_verf,
CASE WHEN a.comm = b.comm THEN 'MATCHED'
WHEN a.comm = c.comm THEN 'MATCHED'
ELSE 'UNMATCHED'
END as Matched
from tblA a
left join tblB b
on a.account = b.account
and a.uniq_id = b.uniq_id;
left join tblB c
on a.account = c.account
and a.uniq_id = c.uniq_id;

Answer 3

Yet another option could be something like
SELECT a.account, a.uniq_id, a.pay, bc.pay as pay_verf, a.comm, bc.comm as comm_verf
FROM a left join (
SELECT * from b
UNION ALL
SELECT * from c
) bc on (a.account = bc.account and a.uniq_id = bc.uniq_id)