Better query for ASSOCIATION_ids

For has_many relations Imagine we have 2 models: Cart and Item. Cart has many Items.

If we execute the following statement

Cart.first.item_ids

we get the following query

SELECT * FROM `items` WHERE (`items`.cart_id = 1)

This could by retrieving only an array, and not the objects.

SELECT `items`.id FROM `items` WHERE (`items`.cart_id = 1)

For has_many :through relations Imagine 3 models: User, Membership, Account

The User has many accounts trough membership and vice versa. We define the fitted relations and Execute the following query

User.first.account_ids

This will create the following query

SELECT `accounts`.* FROM `accounts` INNER JOIN memberships ON accounts.id = memberships.account_id WHERE ((`memberships`.user_id = 1))

While the following query would be a lot more efficient (only retrieving an array, not the objects):

SELECT `memberships`.account_id FROM memberships WHERE ((`memberships`.user_id = 1))

What do you think?