在SQL中向查询添加子查询

Question

I have a query that works very well. Let me start with it:

Edit: The SQL has been updated. I get 0 in every row.

   SELECT i.item, i.user_id, u.username,
        (COALESCE(r.ratetotal, 0)) AS total,
        (COALESCE(c.commtotal, 0)) AS comments,
        (COALESCE(r.rateav, '50%')) AS rate,
        (COALESCE(x.wasRated, '0')) AS wasRated
        FROM items AS i
        LEFT JOIN master_cat AS c
            ON (c.cat_id = i.cat_id)
        LEFT JOIN users AS u 
        ON u.user_id = i.user_id    
        LEFT JOIN
            (SELECT item_id, 
            COUNT(item_id) AS ratetotal, 
            AVG(rating) AS rateav 
            FROM ratings GROUP BY item_id) AS r 
        ON r.item_id = i.item_id
        LEFT JOIN
            (SELECT item_id, 
            COUNT(item_id) AS commtotal 
            FROM reviews GROUP BY item_id) AS c
        ON c.item_id = i.item_id
        LEFT JOIN
            (SELECT xu.user_id, ra.item_id, '1' AS wasRated
            FROM users AS xu
            LEFT JOIN ratings AS ra
                ON ra.user_id = xu.user_id
            WHERE xu.user_id = '1') AS x 
         ON x.user_id = u.user_id
              AND x.item_id = r.item_id
        WHERE c.category = 'Movies' 
        ORDER by i.item ASC;

I need to add one more function to it, where you see AS x

Basically, there are three tables here that are important. items , reviews and ratings . In the top portion you see there are subqueries that are taking statistics such as averages and totals for each item.

I need a final query that is tied to user_id , item_id and rate_id (in ratings ). In the end result, where it list each item and the stats with it, I want one more column, a simple true or false if logged in user has rated it. So I need something like this:

SELECT ???
FROM ratings AS r
WHERE r.user_id = '{$user_id}'

( user_id of logged in user is passed in from PHP.`)

How can I make a subquery that gives me that last bit of info, but puts it in each row of items in the parent query?

Answer 1

Add this to the parent query.

, coalesce(x.WasRated, 'false') as WasRated

Your x subquery is:

(select users.user_id
 , ratings.item_id
, 'true' WasRated
from users join ratings on user.user_id = ratings.user_id
where users.user_id = the one for the logged in user
) x on x.user_id = users.user_id
and x.item_id = ratings.item_id

or something like it.