If no rows satisfy the condition, then Oracle inserts the row into the target table based on the corresponding MERGE source row.
merge_update_clause - The merge_update_clause is used to specify the update column values of the target table.
Oracle performs the specified update if the condition of the ON clause is true.
As with any normal update, when the update clause is executed, all update triggers defined on the target table are fired.
If the condition is false, the update operation is skipped when merging the row into the target table.