Question

I’m writing a query for an application that needs to list all the products with the number of times they have been purchased.

I came up with this and it works, but I am not too sure how optimized it is. My SQL is really rusty due to my heavy usage of ORM’s, But in this case a query is a much more elegant solution.

Can you spot anything wrong (approach wise) with the query?

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SELECT  products.id,          products.long_name AS name,          count(oi.order_id) AS sold FROM    products LEFT OUTER JOIN        ( SELECT * FROM orderitems         INNER JOIN orders ON orderitems.order_id = orders.id          AND orders.paid = 1 ) AS oi        ON oi.product_id = products.id GROUP BY products.id 

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The schema (with relevant fields) looks like this:

*orders*      id, paid *orderitems*  order_id, product_id *products*    id 

UPDATE

This is for MySQL

Answer 1

I’m not sure about the ‘(SELECT *’ … business.

This executes (always a good start) and I think is equivalent to what was posted.

SELECT  products.id,      products.long_name AS name,      count(oi.order_id) AS sold FROM    products LEFT OUTER JOIN     orderitems AS oi         INNER JOIN              orders              ON oi.order_id = orders.id AND orders.paid = 1     ON oi.product_id = products.id GROUP BY products.id