how to calculate unique column values in mysql

Question

Here is my data

cardNo| userName| tablename| hours |  date 
1     |  a      |    a     |   12  |  12-06-2015 
1     |  a      |    a     |    5  |  11-06-2015 
2         


        

Answer 1

It's simple SUM() with GROUP BY:

SELECT cardNo,sum(hours) 
FROM yourtable
GROUP BY cardNo;

I left it as an exercise for the OP to include userName and tablename columns into the query