如何进行合并重复的主键的SELECT

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;