I have two tables with data schemed as below:
Code:
invoice_items
      | ii_id | invoice_id | item_id | item_ref | item_quantity | item_price |
      
      pricelist
 | item_id | ref | part | description | price | cost |
I want to retreive the sum ( invoice_items.item_quantity * pricelist.cost ) for each invoice_item.item_id. I tried this:

Code:
SELECT SUM( pl.cost ) AS totalCost
     FROM pricelist pl
 LEFT JOIN invoice_items inv ON inv.item_id = pl.item_id
but I think it gave me a cartesian product since the sum returned was huge.

But when I did this ( which is what actually what I needed ):
Code:
SELECT SUM( pl.cost * inv.item_quantity ) AS totalCost
      FROM pricelist pl
      LEFT JOIN invoice_items inv ON inv.item_id = pl.item_id
I think I came up with the right figure.

Retreiving the correct sum is very important. So my question is: Is the second query written correctly, and if not, what should be the correct way to write it?

Thanks