SQL - sum of some rows, minus sum of other rows

Question

I have a table in mySQL with the following columns:

CUSTOMER_CODE | TRANS_TYPE | TRANS_VALUE

TRANS_TYPE could be either \"DRINV\" (a sale) or \

Answer 1

Yes, it is possible. Use CASE caluse:

SELECT CUSTOMER_CODE,
SUM(CASE WHEN TRANS_TYPE = 'DRINV' THEN TRANS_VALUE ELSE (- TRANS_VALUE) END ) as SALES
FROM DR_TRANS GROUP BY CUSTOMER_CODE