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To anyone who is wondering why simple inner join and performing sum() using group by does not work: One of the reason is, the set of challenge_ids in View_Stats does not equal to the set of challenge_ids in Submission_Stats. Therefore, using simple inner join to join stats data with the contest table will lead to missing records. It's not your fault.
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To anyone who is wondering why simple inner join and performing sum() using group by does not work: One of the reason is, the set of challenge_ids in View_Stats does not equal to the set of challenge_ids in Submission_Stats. Therefore, using simple inner join to join stats data with the contest table will lead to missing records. It's not your fault.