The MERGE-INTO statement with the DELETE clause deletes the target table rows for which the condition evaluates to true. The source_table_name following the USING keyword specifies the target table for deletes.
WHEN MATCHED THEN can include either UPDATE or DELETE, but not both.
If you specify DELETE, you cannot specify INSERT.
If the DELETE clause is specified and there is a DELETE trigger defined on the target object, the MERGE-INTO statement can act as the triggering event for the DELETE trigger.