Join table on conditions, count on conditions - sql

Question

SELECT *, null AS score,
'0' AS SortOrder
FROM products
WHERE datelive = -1
AND hidden = 0
UNION
SELECT e.*, (SUM(r.a)/(COUNT(*)*1.0)+
SUM(r.b)/(COUNT(*)*1.0)+
SUM(r.c)/(COUNT(*)*1.0)+
SUM(r.d)/(COUNT(*)*1.0))/4 AS score,
'1' AS SortOrder
FROM products e
LEFT JOIN reviews r
ON r.productID = e.productID
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID
HAVING COUNT(*) >= 5
UNION
SELECT e.*, (SUM(r.a)/(COUNT(*)*1.0)+
SUM(r.b)/(COUNT(*)*1.0)+
SUM(r.c)/(COUNT(*)*1.0)+
SUM(r.d)/(COUNT(*)*1.0))/4 AS score,
'2' AS SortOrder
FROM products e
LEFT JOIN reviews r
ON r.productID = e.productID
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID
HAVING COUNT(*) < 5
ORDER BY SortOrder ASC, score DESC
This creates an SQL object for displaying products on a page. The first request grabs items of type datelive = -1, the second of type datelive != -1 but r.count(*) >= 5, and the third of type datelive != -1 and r.count(*) < 5. The reviews table is structured similar to the below:
reviewID | productID | a | b | c | d | approved
-------------------------------------------------
1 1 5 4 5 5 1
2 5 3 2 5 5 0
3 2 5 5 4 3 1
... ... ... ... ... ... ...
I'm trying to work it such that r.count(*) only cares for rows of type approved = 1, since tallying data based on unapproved reviews isn't ideal. How can I join these tables such that the summations of scores and the number of rows is dependent only on approved = 1?
I've tried adding in AND r.approved = 1 in the WHERE conditional for the joins and it doesn't do what I'd like. It does sort it properly, but then it no longer includes items with zero reviews.

Answer 1

You seem to be nearly there.
In your question you talked about adding the AND r.approved = 1 to the join criteria but by the sounds of it you are actually adding it to the WHERE clause.
If you instead properly add it to the join criteria like below then it should work fine:
SELECT *, null AS score,
'0' AS SortOrder
FROM products
WHERE datelive = -1
AND hidden = 0
UNION
SELECT e.*, (SUM(r.a)/(COUNT(*)*1.0)+
SUM(r.b)/(COUNT(*)*1.0)+
SUM(r.c)/(COUNT(*)*1.0)+
SUM(r.d)/(COUNT(*)*1.0))/4 AS score,
'1' AS SortOrder
FROM products e
LEFT JOIN reviews r ON r.productID = e.productID
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID
HAVING COUNT(*) >= 5
UNION
SELECT e.*, (SUM(r.a)/(COUNT(*)*1.0)+
SUM(r.b)/(COUNT(*)*1.0)+
SUM(r.c)/(COUNT(*)*1.0)+
SUM(r.d)/(COUNT(*)*1.0))/4 AS score,
'2' AS SortOrder
FROM products e
LEFT JOIN reviews r ON r.productID = e.productID AND r.approved = 1
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID
HAVING COUNT(*) < 5
ORDER BY SortOrder ASC, score DESC
SQL Fiddle here.
Notice again how I have simply put the AND r.approved = 1 directly after LEFT JOIN reviews r ON r.productID = e.productID which adds an extra criteria to the join.
As I mentioned in my comment, the WHERE clause will filter rows out of the combined record set after the join has been made. In some cases the RDBMS may optimise it out and put it into the join criteria but only where that would make no difference to the result set.

Answer 2

Calculating the non-zero sums and joining it to your result may solve it;
fiddle
SELECT a.productID,
NULL AS score,
'0' AS SortOrder
FROM products a
WHERE datelive = -1
AND hidden = 0
UNION
SELECT e.productID,
(min(x.a)/(min(x.cnt)*1.0)+ min(x.b)/(min(x.cnt)*1.0)+ min(x.c)/(min(x.cnt)*1.0)+ min(x.d)/(min(x.cnt)*1.0))/4 AS score,
'1' AS SortOrder
FROM products e
JOIN reviews r ON r.productID = e.productID
LEFT JOIN
(SELECT ee.productID,
sum(rr.a) AS a,
sum(rr.b) AS b,
sum(rr.c) AS c,
sum(rr.d) AS d,
count(*) AS cnt
FROM products ee
LEFT JOIN reviews rr ON ee.productID = rr.productID
GROUP BY ee.productID) x ON e.productID = x.productID
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID HAVING COUNT(*) >= 5
UNION
SELECT e.productID,
(min(x.a)/(min(x.cnt)*1.0)+ min(x.b)/(min(x.cnt)*1.0)+ min(x.c)/(min(x.cnt)*1.0)+ min(x.d)/(min(x.cnt)*1.0))/4 AS score,
'2' AS SortOrder
FROM products e
LEFT JOIN reviews r ON r.productID = e.productID
LEFT JOIN
(SELECT ee.productID,
sum(rr.a) AS a,
sum(rr.b) AS b,
sum(rr.c) AS c,
sum(rr.d) AS d,
count(*) AS cnt
FROM products ee
LEFT JOIN reviews rr ON ee.productID = rr.productID
GROUP BY ee.productID) x ON e.productID = x.productID
WHERE e.hidden = 0
AND e.datelive != -1
GROUP BY e.productID HAVING COUNT(*) < 5
ORDER BY SortOrder ASC,
score DESC

Answer 3

You could create a temp table that only contains rows where approved = 1, and then join on the temp table instead of reviews.
create table tt_reviews like reviews;
insert into tt_reviews
select * from reviews
where approved = 1;
alter table tt_reviews add index(productID);
Then replace reviews with tt_reviews in your above query.