MySQL选择行大于一的地方

Question

I am working on a query that is joining multiple tables to drill down to get the number of subscribers who voted by region where subscribers have more than one vote.

The issue I am stuck at is trying to write in the query of figuring out the calculation of where subscribers voted more than one.

SELECT COUNT(*), regions.name, 
(SELECT COUNT(*) FROM votes 
LEFT JOIN profiles on votes.subscriber_id = profiles.subscriber_id 
LEFT JOIN countries on profiles.country_id = countries.id 
WHERE countries.region_id = regions.id GROUP BY votes.subscriber_id) as vote_count 
FROM subscribers
LEFT JOIN profiles on subscribers.id = profiles.subscriber_id
LEFT JOIN countries on profiles.country_id = countries.id
LEFT JOIN regions on countries.region_id = regions.id 
LEFT JOIN votes on subscribers.id = votes.subscriber_id
WHERE subscribers.created_at < '2011-04-22 00:00:00'
GROUP BY regions.id
HAVING vote_count > 1;

With the above query I am getting the error of, Subquery returns more than 1 row

Any ideas?

Answer 1

The section

SELECT COUNT(*) FROM votes 
LEFT JOIN profiles on votes.subscriber_id = profiles.subscriber_id 
LEFT JOIN countries on profiles.country_id = countries.id 
WHERE countries.region_id = regions.id GROUP BY votes.subscriber_id

is returning more than one result. Try removing the "GROUP BY votes.subscriber_id" which should solve the problem

Answer 2

if your subquery:

(SELECT COUNT(*) FROM votes 
LEFT JOIN profiles on votes.subscriber_id = profiles.subscriber_id 
LEFT JOIN countries on profiles.country_id = countries.id 
WHERE countries.region_id = regions.id GROUP BY votes.subscriber_id)

returns more than 1 row, then it will error, because it's trying to put a collection of rows into the value vote_count . You could solve this by guaranteeing the query has only 1 row result by adding a HAVING clause.

Answer 3

Since you place the sub query in the SELECT part of the query, only one return value is expected (since result sets are two dimensional).

You have to add somewhere in the inner query's WHERE clause a match to the outer query to make sure only one row matches.

What COUNT(*) is it you're looking for that matches regions.name? You have to connect the inner query to that.

Answer 4

Try putting the HAVING vote_count > 1 clause in the subquery. Also, try the subquery on its own to see what it's yielding.