相关表的SUM列

Question

I've two tables, packages:

id, ..., price fields

and users:

id, ..., package_id

so every user has a package (users can have same package) that has a price.

and I want to calculate the SUM of the price of all users, how is the best way to do this? preferably with only SQL. Having in mind that users table can have ~1m of users.

Answer 1

SELECT SUM(price_x_user)
FROM (
    SELECT price AS price_x_user,
        users.id
    FROM users
    INNER JOIN packages ON packages.id = users.package_id
) AS users_package

Answer 2

Select id, SUM(price) from users t
Left join package p on p.id = t.id
group by t.id

When using a grouping function like SUM, it is required to group by.