Oracle9i引入了MERGE命令,你能够在一个SQL语句中对一个表同时执行inserts和updates操作. MERGE命令从一个或多个数据源中选择行来updating或inserting到一个或多个表.在Oracle 10g中MERGE有如下一些改进：

你能够添加WHERE子句到UPDATE或INSERT子句中去, 来跳过update或insert操作对某些行的处理. 下面例子根据表NEWPRODUCTS来更新表PRODUCTS数据, 但必须字段CATEGORY也得同时匹配上:

DE>SQL> MERGE INTO products p

2 USING newproducts np

3 ON (p.product_id = np.product_id)

4 WHEN MATCHED THEN

5 UPDATE

6 SET p.product_name = np.product_name

7 WHERE p.category = np.category;

2 rows merged.

SQL> SELECT * FROM products;

PRODUCT_ID PRODUCT_NAME CATEGORY

---------- -------------------- ----------

1501 VIVITAR 35MM ELECTRNCS

1502 OLYMPUS CAMERA ELECTRNCS

1600 PLAY GYM TOYS

1601 LAMAZE TOYS

1666 HARRY POTTER DVD

SQL>

SQL> rollback;DE>

在这个例子中, 产品ID为1502,1601和1666匹配ON条件但是1666的category不匹配. 因此MERGE命令只更新两行数据. 下面例子展示了在Updates和Inserts子句都使用WHERE子句:

DE>SQL> MERGE INTO products p

2 USING newproducts np

3 ON (p.product_id = np.product_id)

4 WHEN MATCHED THEN

5 UPDATE

6 SET p.product_name = np.product_name,

7 p.category = np.category

8 WHERE p.category = 'DVD'

9 WHEN NOT MATCHED THEN

10 INSERT

11 VALUES (np.product_id, np.product_name, np.category)

12 WHERE np.category != 'BOOKS'

SQL> /

1 row merged.

SQL> SELECT * FROM products;

PRODUCT_ID PRODUCT_NAME CATEGORY

---------- -------------------- ----------

1501 VIVITAR 35MM ELECTRNCS

1502 OLYMPUS IS50 ELECTRNCS

1600 PLAY GYM TOYS

1601 LAMAZE TOYS

1666 HARRY POTTER TOYS

SQL>DE>

注意由于有WHERE子句INSERT没有插入所有不匹配ON条件的行到表PRODUCTS.

3、无条件的Inserts

你能够不用连接源表和目标表就把源表的数据插入到目标表中. 这对于你想插入所有行到目标表时是非常有用的. Oracle 10g现在支持在ON条件中使用常量过滤谓词. 举个常量过滤谓词例子ON (1=0). 下面例子从源表插入行到表PRODUCTS, 不检查这些行是否在表PRODUCTS中存在:

DE>SQL> MERGE INTO products p

2 USING newproducts np

3 ON (1=0)

4 WHEN NOT MATCHED THEN

5 INSERT

6 VALUES (np.product_id, np.product_name, np.category)

7 WHERE np.category = 'BOOKS'

SQL> /

1 row merged.

SQL> SELECT * FROM products;

PRODUCT_ID PRODUCT_NAME CATEGORY

---------- -------------------- ----------

1501 VIVITAR 35MM ELECTRNCS

1502 OLYMPUS IS50 ELECTRNCS

1600 PLAY GYM TOYS

1601 LAMAZE TOYS

1666 HARRY POTTER DVD

1700 WAIT INTERFACE BOOKS

6 rows selected.

SQL>DE>

4、新增加的DELETE子句

Oracle 10g中的MERGE提供了在执行数据操作时清除行的选项. 你能够在WHEN MATCHED THEN UPDATE子句中包含DELETE子句. DELETE子句必须有一个WHERE条件来删除匹配某些条件的行.匹配DELETE WHERE条件但不匹配ON条件的行不会被从表中删除.

下面例子验证DELETE子句. 我们从表NEWPRODUCTS中合并行到表PRODUCTS中, 但删除category为ELECTRNCS的行.

DE>SQL> MERGE INTO products p

2 USING newproducts np

3 ON (p.product_id = np.product_id)

4 WHEN MATCHED THEN

5 UPDATE

6 SET p.product_name = np.product_name,

7 p.category = np.category

8 DELETE WHERE (p.category = 'ELECTRNCS')

9 WHEN NOT MATCHED THEN

10 INSERT

11 VALUES (np.product_id, np.product_name, np.category)

SQL> /

4 rows merged.

SQL> SELECT * FROM products;

PRODUCT_ID PRODUCT_NAME CATEGORY

---------- -------------------- ----------

1501 VIVITAR 35MM ELECTRNCS

1600 PLAY GYM TOYS

1601 LAMAZE TOYS

1666 HARRY POTTER TOYS

1700 WAIT INTERFACE BOOKS

SQL>DE>