SQL计数并从多个表联接

Question

There is a product table which contains all the product details. A product can be nominated to the popular table from where different people can vote on it. i need to count only the votes of registered users. Currently it is counting all the votes that a particular product has. How do i overcome this problem? i have pasted my sql code below:

SELECT popular.name, popular.product_id, product.text, product.author, count(        vote.product_id ) AS votes
FROM popular
LEFT JOIN product ON ( product.id = popular.product_id )
LEFT JOIN vote ON ( vote.product_id = popular.product_id )
where popular.hidden = '1' and
popular.name in (select registered.name from registered 
where registered.course_id='".$course_id."' and 
registered.section = '".$section."' and 
registered.term = '".$term."')
GROUP BY popular.product_id
ORDER BY votes DESC Limit 10

Answer 1

SELECT pop.product_id, pd.text, count( vt.product_id ) AS votes
FROM popular pop
LEFT JOIN product pd ON(pd.product = pop.product_id)
LEFT JOIN vote vt ON(vt.product_id = pop.product_id)
WHERE 1 = 1 // or pop.product_id = yourProductId here
GROUP BY pop.product.id
ORDER BY vt.votes DESC

Answer 2

You're missing a join between votes and your other tables

Select P.ID, P.text, count(v.Product_ID) as votes
FROM Product PRO
LEFT JOIN Popular Pop
  ON PRO.ID = Pop.Product_ID
LEFT JOIN VOTE V   --<-- This is missing
  on V.Product_ID = Pro.ID
Group by P.ID, Pro.Text
order by votes Desc

Answer 3

SELECT popular.product_id, product.text, count( vote.product_id ) AS votes
FROM popular, product, vote
WHERE product.id = popular.product_id AND product.id = vote.product_id
GROUP BY product.id
ORDER BY votes DESC

Note that this query does not return products having no votes. If there are such records in your DB, you should LEFT JOIN with vote table.