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?

  • Do you also require new inventory items to be inserted into the current table from the new table?
    – Philᵀᴹ
    Commented Mar 2, 2015 at 9:08
  • Is there a unique constraint on ItemName, in both tables? Commented Mar 2, 2015 at 11:50

1 Answer 1


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
  SELECT itemname, quantity
  FROM shipment
) ship ON (ship.itemname = inventory.itemname)
    SET inventory.quantity = ship.quantity + inventory.quantity;

Example SQL Fiddle here if you want to play.

  • Nice. The first may need adjustments, if the items appear multiple times in shipment (or none, so nulls will appear due to SUM). Something like: SET quantity = quantity + COALESCE( ( SELECT SUM(s.quantity) FROM shipment s WHERE s.itemname = i.itemname ), 0); Commented Mar 11, 2015 at 9:14

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