Question

I have 2 tables. Problem and problem_votes. There are many rows in the problems table and just one in the votes table.

I have this query:

select
   problems.problem_id,
   creator_member_id,
   problem_title,
   problem_description,
   sum( vote ) as totalVotes,
   problem_date
from problems 
left join problem_votes on
problems.problem_id = problem_votes.problem_id

I expected there to be returned a list of problems, but I only get one item for some reason.

If I take out the sum function, it returns twenty rows. Is there a way to get the query to get the sum of the votes for each problem?

Answer 1

You need a GROUP BY otherwise it will aggregate the entire table instead of returning one row for each problem_id:

SELECT
    problems.problem_id,
    creator_member_id,
    problem_title,
    problem_description,
    sum(vote) as totalVotes,
    problem_date
FROM problems
LEFT JOIN problem_votes
    ON problems.problem_id = problem_votes.problem_id
GROUP BY problems.problem_id

This query uses a MySQL extension: GROUP BY and HAVING with Hidden Columns