## Calculating the difference between result columns

From: "Keith Worthington" "PostgreSQL Novice" Calculating the difference between result columns 2004-12-27 21:46:15 20041227214615.M20847@narrowpathinc.com (view raw, whole thread or download thread mbox) 2004-12-27 21:46:15 from "Keith Worthington"  2004-12-28 15:00:35 from Tom Lane  2004-12-28 16:41:01 from Sudamericano pgsql-novice
```Hi All,

I'm stuck again.  I have written two queries.  The first calculates the total
quantity of items that have been ordered.  The second calculates the total
quantity of items that have been received.  Now I want to find the difference
which will tell me what is still on order.  Any hints would be appreciated.

SELECT purchase_order.tbl_line_item.item_id,
sum( purchase_order.tbl_line_item.quantity ) AS ordered
FROM purchase_order.tbl_line_item
JOIN purchase_order.tbl_detail
USING (po_number)
WHERE NOT purchase_order.tbl_detail.closed
GROUP BY purchase_order.tbl_line_item.item_id;

SELECT purchase_order.tbl_line_item.item_id,
FROM purchase_order.tbl_line_item
JOIN purchase_order.tbl_receiving
ON ( purchase_order.tbl_line_item.po_number =
purchase_order.tbl_receiving.po_number AND
purchase_order.tbl_line_item.po_line =
purchase_order.tbl_receiving.po_line )
JOIN purchase_order.tbl_detail
ON ( purchase_order.tbl_line_item.po_number =
purchase_order.tbl_detail.po_number)
WHERE NOT purchase_order.tbl_detail.closed
GROUP BY purchase_order.tbl_line_item.item_id;

Kind Regards,
Keith

______________________________________________
99main Internet Services http://www.99main.com

```

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