Join table with MAX value from another

Question

select * from order
-------------------
|orderID|productID|
-------------------
|  1    |  234    |
|  2    |  234    |
|  3    |  123    |
-------------------

select *         


        

Answer 1

when you need to use aggregate you must use group by and in compare condtion use Having

 SELECT orderID, productID, MAX(cost_price)
 FROM order LEFT JOIN product_supplier 
 ON order.productID=product_supplier.productID having cost_price=MAX(cost_price) group by productID ;