sql subquery, passing a variable

Question

Can you pass variables into subqueries, like so?

SELECT users.id AS id, 
(SELECT SUM(total) FROM (image_totals) WHERE `cat_id` IN ('5', '3') AND `user_id` =id) AS image_count

This is only part of a larger query, all being generated through Active Record, but the key issue remains, the 'id' variable, how can I pass this into my subquery? Am I looking at this all wrong?

Thanks in advance. And let me know if you need more info.

Answer 1

If I understood your question correctly, then yes you can.

If the tables don't contain the same columns then you don't need the table name for each column. I prefer to include the table name as it makes it easier to understand.

SELECT  users.id AS id ,
        (SELECT SUM(image_totals.total)
         FROM   image_totals
         WHERE  image_totals.cat_id IN ( '5', '3' ) AND 
                image_totals.user_id = users.id) AS image_count
FROM users

you can also use alias' for tables to make it a bit easier to type. u = user and i = image_totals.

SELECT  u.id AS id ,
        (SELECT SUM(i.total)
         FROM   image_totals AS i
         WHERE  i.cat_id IN ( '5', '3' ) AND 
                i.user_id = u.id) AS image_count
FROM users AS u

Answer 2

nope, that is impossible, it will have to be implemented differently.

Select has to be selecting from one consistent dataset.

Your dataset may contain complex queries.

Answer 3

Use GROUP BY. You want SUM(total) for each user.id for particular values of cat_id. I don't know what the rest of your query looks like, but for what was shown, you can just:

SELECT
        users.id AS id,
        SUM(total)
FROM image_totals
WHERE cat_id IN ('5', '3')
GROUP BY users.id