Oracle SQL Summing Values From Two Different Tables Hey all so I am trying to add to (or subtract from) a column of different values based on a separate column in another table. Here is a example of what I am tying to do:

Table 1: (Current Inventory)

ItemName  |  Quantity
----------|----------
Baseball  |         5
Football  |        10
Jersey    |         3


Table 2: (New Shipment)

ItemName  |  Quantity
----------|----------
Baseball  |        70
Football  |       100
Jersey    |        50


How can I update my all items in Table 1 (current inventory) by adding Table 2's quantity to them?
You can do this using an UPDATE:

UPDATE inventory i
   SET quantity = ( SELECT s.quantity+i.quantity 
                     FROM shipment s
                    WHERE s.itemname = i.itemname );


or a MERGE:

MERGE INTO inventory
USING 
(
  SELECT itemname, quantity
  FROM shipment
) ship ON (ship.itemname = inventory.itemname)
WHEN MATCHED THEN UPDATE 
    SET inventory.quantity = ship.quantity + inventory.quantity;


Example SQL Fiddle here if you want to play.