Question

Very simple question (for some): is it possible to use select subquery result in where clause?

I’m currently using something like this:

SELECT companies.id
    , companies.name
    , (SELECT COUNT(*)
    FROM orders
    WHERE
        orders.company_id = companies.id
        AND
        orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
    ) AS number_of_rides
FROM companies
WHERE
    (SELECT COUNT(*)
    FROM orders
    WHERE
        orders.company_id = companies.id
        AND
        orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
    ) != 0
    AND
    companies.affiliate = 0
    AND
    companies.id = 346

This makes the same query run twice, once in select and the other in where. Is it possible at all to reference the select subquery in where to look something like this:

SELECT companies.id
    , companies.name
    , (SELECT COUNT(*) AS number_of_rides
    FROM orders
    WHERE
        orders.company_id = companies.id
        AND
        orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
    ) AS x
FROM companies
WHERE
    x.number_of_rides != 0
    AND
    companies.affiliate = 0

This doesn’t work at the moment, neither does this:

SELECT companies.id
    , companies.name
    , (SELECT COUNT(*)
    FROM orders
    WHERE
        orders.company_id = companies.id
        AND
        orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
    ) AS number_of_rides
FROM companies
WHERE
    number_of_rides != 0
    AND
    companies.affiliate = 0

Is it possible at all without running it twice in the query?

Edit: OK. Although using GROUP BY wouldn’t be possible in some cases, it did what I needed to achieve in this case. That’s what I did:

SELECT companies.id
    , companies.name
    , (SELECT COUNT(*)
    FROM orders
    WHERE
        orders.company_id = companies.id
        AND
        orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
    ) AS number_of_rides
FROM companies
WHERE
    companies.affiliate = 0
GROUP BY companies.id
HAVING number_of_rides != 0

I would still like to know if there’s a technical explanation as to why WHERE can’t access the subquery result in SELECT and HAVING can…

Answer 1

Try this

Select 
    companies.id  , 
    companies.name,
    Tcount as number_of_rides
FROM companies
left join (
        select 
            id , 
            COUNT(*) as Tcount 
        FROM orders 
        where orders.scheduled_at BETWEEN '2012-08-01 00:00:00' AND '2012-10-31 23:59:59'
        ) as orders on orders.company_id = companies.id
WHERE companies.affiliate = 0 AND companies.id = 346
group by companies.id 
having number_of_rides != 0