Question

I have this query:

select problems.problem_id , creator_member_id , problem_title , problem_description , sum( vote ) as totalVotes , DAYOFMONTH(problem_date) , DAYNAME(problem_date) , YEAR(problem_date) , MONTH(problem_date) , first_name , last_name , email , small_thumb , mid_thumb 
    from problems 
        left join problem_votes 
            on problems.problem_id = problem_votes.problem_id 
        left join users 
            on problems.creator_member_id = users.user_id 
        left join member_photo 
            on problems.creator_member_id = member_photo.member_id 
    where problems.problem_id = 1;

It matches nothing, and returns this:

-+--------------------+---------------------+------------+-----------+-------+-------------+-----------+
| problem_id | creator_member_id | problem_title | problem_description | totalVotes | DAYOFMONTH(problem_date) | DAYNAME(problem_date) | YEAR(problem_date) | MONTH(problem_date) | first_name | last_name | email | small_thumb | mid_thumb |
+------------+-------------------+---------------+---------------------+------------+--------------------------+-----------------------+--------------------+---------------------+------------+-----------+-------+-------------+-----------+
|       NULL |              NULL | NULL          | NULL                |       NULL |                     NULL | NULL                  |               NULL |                NULL | NULL       | NULL      | NULL  | NULL        | NULL      |
+------------+-------------------+---------------+---------------------+------------+--------------------------+-----------------------+--------------------+---------------------+------------+-----------+-------+-------------+-----------+

But I wonder why it returns anything at all? Is there something wrong with the schema? Or the query?

I am checking whether it returns nothing, and trying to return 404 page, but the system thinks there is 1 returned row, so it confuses my application.

Anything I might be doing wrong here?

Thanks!!

Answer 1

Try adding the following clause to the end of your query:

GROUP BY problems.problem_id, creator_member_id, problem_title, 
problem_description, problem_date, first_name, last_name, 
email, small_thumb ,mid_thumb 

Best practice is that every column that is selected but not aggregated (like vote) must be in the group by clause, though MYSQL does not enforce this. Instead, it behaves strangely and confuses people. (See this answer for a better explanation.)