1, 能嵌入delete语句

2, update, insert语句能嵌入where clause

3, update语句与insert语句，不必同时出现，是可选的（optional）

http://www.oracle-base.com/articles/10g/MergeEnhancements10g.php

MERGE Statement Enhancements in Oracle Database 10g

Oracle 10g includes a number of amendments to the MERGE statement making it more flexible.

• Test Table
• Optional Clauses
• Conditional Operations
• DELETE Clause

Test Table

The following examples use the table defined below.

CREATE TABLE test1 AS
SELECT *
FROM   all_objects
WHERE  1=2;

Optional Clauses

The MATCHED and NOT MATCHED clauses are now optional making all of the following examples valid.

-- Both clauses present.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status
  WHEN NOT MATCHED THEN
    INSERT (object_id, status)
    VALUES (b.object_id, b.status);

-- No matched clause, insert only.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN NOT MATCHED THEN
    INSERT (object_id, status)
    VALUES (b.object_id, b.status);

-- No not-matched clause, update only.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status;

Conditional Operations

Conditional inserts and updates are now possible by using a WHERE clause on these statements.

-- Both clauses present.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status
    WHERE  b.status != 'VALID'
  WHEN NOT MATCHED THEN
    INSERT (object_id, status)
    VALUES (b.object_id, b.status)
    WHERE  b.status != 'VALID';

-- No matched clause, insert only.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN NOT MATCHED THEN
    INSERT (object_id, status)
    VALUES (b.object_id, b.status)
    WHERE  b.status != 'VALID';

-- No not-matched clause, update only.
MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status
    WHERE  b.status != 'VALID';

DELETE Clause

An optional DELETE WHERE clause can be used to clean up after a merge operation. Only those rows which match both the ON clause and the DELETE WHERE clause are deleted.

MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status
    WHERE  b.status != 'VALID'
  DELETE WHERE (b.status = 'VALID');