Question

When I run this query, the votes sum is 2 times what it should be (sum=6 instead of 3). Can someone figure out the fix for this?

SELECT sum(votes.vote) AS sum
    , my_votes.vote IS NOT NULL AS did_i_vote
    , votes.parent_id, subject
    , review_date
    , item_id
    , review_summary
    , review, full_name
    , reputation
    , profile_picture
    , accounts.acct_id
FROM votes
RIGHT JOIN items_purchased 
    on votes.parent_id=items_purchased.purchase_id 
JOIN accounts 
    ON items_purchased.purchaser_account_id=accounts.acct_id  
JOIN items 
    on items_purchased.item_id=items.folder_id
LEFT JOIN votes AS my_votes 
    ON my_votes.parent_id=items_purchased.purchase_id 
    AND my_votes.acct_id='3' 
    AND my_votes.column_name='purchase_id' 
WHERE purchase_id='2' 
    AND deleted_p!=1 and pub_priv_p!=1                                       
GROUP BY items_purchased.purchase_id

I’m pretty sure it has to do with the JOINs because if I get rid of JOIN items on items_purchased.item_id=items.folder_id then the sum=3. However, I need that JOIN in there somehow.

Thoughts?

Answer 1

Without a schema we can’t tell, but this is a guess:

Check all of your join conditions – you’re likely missing a condition causing that set of results to be ‘duplicated’.

For example, if I have a table

`Foo` with columns `A` `B` and `C` - A and B are the PK;
`Bar` with columns `A` `B` and `Z` - A and B are the PK;
`Biz` with columns `Z` `GOAL` 

And I wanted to count the number of GOALS per A, if I joined the Foo to Bar just using A and not B as well, I would likely get an erroneous count.

The easiest way to see this is to do a SELECT * and remove the group by