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Postgres Pro includes one merge support function that may be used in theRETURNING list of aMERGE command to identify the action taken for each row; seeTable 9.66.

Example:

MERGE INTO products p  USING stock s ON p.product_id = s.product_id  WHEN MATCHED AND s.quantity > 0 THEN    UPDATE SET in_stock = true, quantity = s.quantity  WHEN MATCHED THEN    UPDATE SET in_stock = false, quantity = 0  WHEN NOT MATCHED THEN    INSERT (product_id, in_stock, quantity)      VALUES (s.product_id, true, s.quantity)  RETURNING merge_action(), p.*; merge_action | product_id | in_stock | quantity--------------+------------+----------+---------- UPDATE       |       1001 | t        |       50 UPDATE       |       1002 | f        |        0 INSERT       |       1003 | t        |       10

Note that this function can only be used in theRETURNING list of aMERGE command. It is an error to use it in any other part of a query.