Question

I’m always getting a timed out on the following query:

select * FROM `products` 
where 
    `active`=1 
and `group`=6 
and `id` not in (select `id` from `purcheased` where `userId`=14 and `price`>100 
and `reversed`=0)  
order by `price` asc limit 0,500

This takes 0.01s to execute, and in this particular case returns 0 results:

select `id` from `purcheased` where `userId`=14 and `price`>100 and `reversed`=0 

This executes in .02s:

select * FROM `products` 
where 
    `active`=1 
and `group`= 6 
order by `price` asc limit 0,500 

The full query

select * FROM `products` 
where 
    `active` = 1 
and `group` = 6 
and `id` not in (
                select `id` from `purcheased` 
                where 
                    `userId`=14 
                and `price` > 100 
                and `reversed`=0
                )
order by `price` asc limit 0,500

executes it 60 seconds!

I think this is happening because select id from purcheased … is being executed for each row of the products.

I’m running the queries in mysql.

How do I tell mysql to execute the select id from purcheased once and than to re-use the result?

Answer 1

A LEFT OUTER JOIN is probably your best bet here:

select p.*
from `products` p
left outer join (
    select `id`
    from `purcheased`
    where `userId` = 14 
        and `price` > 100 
        and `reversed` = 0
) pu on p.id = pu.id
where p.`active` = 1 
    and p.`group` = 6 
    and pu.id is null
order by p.`price` 
limit 0, 500