MySQL Select 3 random rows where sum of three rows is less than value

Question

I am trying to select three random rows from a table, where their combined item_price column is less than a desired amount.

Imagine you have an

Answer 1

you can get all triplets of items having sum of price <= 300 with

SELECT a.item_id, a.item_price, b.item_id, b.item_price, c.item_id, c.item_price
  FROM items a 
       JOIN items b ON a.item_id < b.item_id
       JOIN items c ON b.item_id < c.item_id
 WHERE a.item_price + b.item_price + c.item_price <= 300

then you could sort by rand() and pick one.

there are discussions about performance of selecting random rows in mysql that you should check. the triple join will be costly if items table is big.

EDIT

as suggested in other answers, this query can be improved filtering each item by price <= 300, and using an index on items.price.