Question

Short:

From below sql select I get the cart_id and the value of the maximum valued item in that cart.

SELECT CartItems.cart_id, MAX(ItemValues.value) FROM CartItems  INNER JOIN ItemValues  ON CartItems.item_id=ItemValues.item_id GROUP BY CartItems.cart_id 

but I also need item_id for that item (ItemValues.item-id).

Long:

Two tables, CartItems, ItemValues (and their respective Carts, Items, irrelevant here).
Each cart can have several items wheras each item has one value defined in ItemValues.
Each item belongs to one cart.
The value of a cart is the value of the item with maximum value within its cart.
How do I select cart-id, max(item-value) and it’s corresponding item-id?

For instance cart-id A contains item-id X with value 10 and item-id Y with value 90.
With above sql select I get,

A, 90

What I need is

 A, Y, 90 

platform: MS SQL

Answer 1

In MS SQL and Oracle:

SELECT * FROM   (   SELECT ci.*, iv.*,          ROW_NUMBER() OVER (PARTITION BY CartItems.cart_id ORDER BY ItemValues.value DESC)   FROM   CartItems ci   INNER JOIN ItemValues iv      ON CartItems.item_id=ItemValues.item_id   ) s WHERE rn = 1 

In MySQL:

SELECT FROM   (   SELECT ci.*,          (          SELECT id          FROM ItemValues iv          WHERE iv.item_id = ci.item_id          ORDER BY                value DESC          LIMIT 1          ) AS maxitem   FROM   CartItems ci   ) iv, ItemValues ivo WHERE ivo.id = iv.maxitem