how to make a SELECT that merges duplicated Primary Keys - mysql

Question

I'm performing a query that looks like this:
SELECT a.transactionID,a.customerID,b.value
FROM adjustments a
INNER JOIN change b
on a.transactionID = b.transactionID
and a.event_date = b.event_date
and a.event_id = b.event_id
WHERE comment LIKE 'TRANSFER'
ORDER BY a.transactionID;
this query brings the following result:
transactionID | customerID | value
------------------------------------
TRANSFER-001 | CUSTA | -200
TRANSFER-001 | CUSTB | 200
TRANSFER-002 | CUSTC | -150
TRANSFER-002 | CUSTD | 0
TRANSFER-003 | CUSTA | 0
TRANSFER-003 | CUSTC | 150
I need to change this query to bring a list that ignore those cases where the sum of value is 0 for the same transactionID and also, group the customerID and values as following:
transactionID | customerID_A | value_A | customerID_B | value_B
------------------------------------------------------------------
TRANSFER-002 | CUSTC | -150 | CUSTD | 0
TRANSFER-003 | CUSTA | 0 | CUSTC | 150
Can you give any advise about how to solve this?

Answer 1

Try this :
SELECT * FROM (
SELECT a.transactionID,a.customerID,b.value
FROM adjustments a
INNER JOIN change b
on a.transactionID = b.transactionID
and a.event_date = b.event_date
and a.event_id = b.event_id
WHERE comment LIKE 'TRANSFER'
)M
GROUP BY transactionID,customerID,value
HAVING SUM(value) <> 0
ORDER BY transactionID;

Answer 2

SELECT distinct a.transactionID,a.customerID,b.value
FROM adjustments a
INNER JOIN change b
on a.transactionID = b.transactionID
and a.event_date = b.event_date
and a.event_id = b.event_id
WHERE comment LIKE 'TRANSFER'
ORDER BY a.transactionID;
Try distinct at the beginning it will eliminate all the duplicate values.

Answer 3

If I understand correctly, you want conditional aggregation. However, you need to pivot the customers and there is no column for doing that. You can enumerate the customers for each transaction using variables, and use that to pivot the first two customers on the transaction:
SELECT transactionId,
MAX(CASE WHEN seqnum = 1 THEN customerId END) as customer_A,
MAX(CASE WHEN seqnum = 1 THEN value END) as value_A,
MAX(CASE WHEN seqnum = 2 THEN customerId END) as customer_B,
MAX(CASE WHEN seqnum = 2 THEN value END) as value_B
FROM (SELECT a.transactionID, a.customerID, b.value,
(#rn := if(#t = a.transactionID, #rn + 1,
if(#t := a.transactionID, 1, 1)
)
) as seqnum
FROM adjustments a INNER JOIN
change c
ON a.transactionID = c.transactionID AND
a.event_date = c.event_date AND
a.event_id = c.event_id CROSS JOIN
(SELECT #rn := 0, #t := '') params,
WHERE comment LIKE 'TRANSFER'
ORDER BY a.transactionID, b.value DESC
) t
GROUP BY transactionId
HAVING SUM(value) <> 0;