Get sum of rows of customers

Question

How can I get the sum of each customer's hours? My data looks like this

  Customer  |   Hours
   C1       |    15
   C1       |    13
   C3       |    23
   C4       |    10
   C4       |    5

Customer and Hours are in a separate tables. I did my query like this:

SELECT DISTINCT t2.Customer
FROM table1 t1
LEFT JOIN table2 t2
ON t1.id = t2.id
WHERE t2.Customer is not null
ORDER BY t2.Customer ASC

And the result of this is

Customer
C1
C3
C4

I want to do next is to sum the hours of the customers so the output would look like this:

Customer   |    Hours
C1         |    28
C3         |    23
C4         |    15

Answer 1

You want a group by statement, something like this:

SELECT t2.Customer, sum(t1.hours) as hours
FROM table1 t1 LEFT JOIN
     table2 t2
     ON t1.id = t2.id
WHERE t2.Customer is not null
GROUP BY t2.Customer
ORDER BY t2.Customer ASC;