Sum of unique rows of joined table - mysql

Question

I have 3 tables. practices, adjustments and claims.
I need to select all practices with additional column adjustments.amount + count(claims.id)
Here is my query.
SELECT
practices.*,
(
SUM(adjustments.amount) + count(claims.id)
) as accurred_fees
INNER JOIN adjustments ON adjustments.practice_id = practices.id
INNER JOIN claims ON claims.practice_id = practices.id
GROUP BY practices.id
In my database I have 1 practice, 20 claims and 1 adjustment with amount equal to 2. SUM(eligible_fee_adjustments.amount) in query always returns 40, I guess it's 2 * count(claims.id), I don't know why it behaves like that. Could you please help me to find solution. Thanks in advance

Answer 1

You have a problem of joining along two different dimensions, so the rows are multiplying. You can solve this by pre-aggregating the data. The following will fix this particular problem:
SELECT p.*,
(SUM(a.amount) + c.cnt) as accurred_fees
FROM practices p INNER JOIN
adjustments a
ON a.practice_id = p.id INNER JOIN
(SELECT practice_id, count(*) as cnt
FROM claims c
GROUP BY practice_id
) c
ON c.practice_id = p.id
GROUP BY p.id;
You should probably preaggregate the adjustments as well:
SELECT p.*,
(a.amount + c.cnt) as accurred_fees
FROM practices p INNER JOIN
(SELECT practice_id, SUM(amount) as amount
FROM adjustments a
GROUP BY practice_id
) a
ON a.practice_id = p.id INNER JOIN
(SELECT practice_id, count(*) as cnt
FROM claims c
GROUP BY practice_id
) c
ON c.practice_id = p.id
GROUP BY p.id;
And you might want to consider LEFT OUTER JOIN rather than INNER JOIN so you get all practices, even those that might be missing adjustments or claims.