PostgreSQL includes one merge support function that may be used in the RETURNING list of a MERGE command to identify the action taken for each row; see Table 9.66.

示例:

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

注意该函数只能用于RETURNING列表中，且仅限于MERGE命令。 在查询的其他部分使用该函数将导致错误。