oracle-merge用法详解

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：


1、UPDATE或INSERT子句是可选的


2、UPDATE和INSERT子句可以加WHERE子句


3、在ON条件中使用常量过滤谓词来insert所有的行到目标表中,不需要连接源表和目标表


4、UPDATE子句后面可以跟DELETE子句来去除一些不需要的行


首先创建示例表：


create table PRODUCTS
                                                (
                                                PRODUCT_ID INTEGER,
                                                PRODUCT_NAME VARCHAR2(60),
                                                CATEGORY VARCHAR2(60)
                                                );
                                                insert into PRODUCTS values (1501, 'VIVITAR 35MM', 'ELECTRNCS');
                                                insert into PRODUCTS values (1502, 'OLYMPUS IS50', 'ELECTRNCS');
                                                insert into PRODUCTS values (1600, 'PLAY GYM', 'TOYS');
                                                insert into PRODUCTS values (1601, 'LAMAZE', 'TOYS');
                                                insert into PRODUCTS values (1666, 'HARRY POTTER', 'DVD');
                                                commit;
                                                create table NEWPRODUCTS
                                                (
                                                PRODUCT_ID INTEGER,
                                                PRODUCT_NAME VARCHAR2(60),
                                                CATEGORY VARCHAR2(60)
                                                );
                                                insert into NEWPRODUCTS values (1502, 'OLYMPUS CAMERA', 'ELECTRNCS');
                                                insert into NEWPRODUCTS values (1601, 'LAMAZE', 'TOYS');
                                                insert into NEWPRODUCTS values (1666, 'HARRY POTTER', 'TOYS');
                                                insert into NEWPRODUCTS values (1700, 'WAIT INTERFACE', 'BOOKS');
                                                commit;
1、可省略的UPDATE或INSERT子句

在Oracle 9i, MERGE语句要求你必须同时指定INSERT和UPDATE子句.而在Oracle 10g, 你可以省略UPDATE或INSERT子句中的一个. 下面的例子根据表NEWPRODUCTS的PRODUCT_ID字段是否匹配来updates表PRODUCTS的信息:
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;
                                                3 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 TOYS
                                                SQL>
                                                SQL> ROLLBACK;
                                                Rollback complete.
                                                SQL>
在上面例子中, MERGE语句影响到是产品id为1502, 1601和1666的行. 它们的产品名字和种 类被更新为表newproducts中的值. 下面例子省略UPDATE子句, 把表NEWPRODUCTS中新的PRODUCT_ID插入到表PRODUCTS中, 对于在两个表中能够匹配上PRODUCT_ID的数据不作任何处理. 从这个例子你能看到PRODUCT_ID=1700的行被插入到表PRODUCTS中.

SQL> MERGE INTO products p
                                                2 USING newproducts np
                                                3 ON (p.product_id = np.product_id)
                                                4 WHEN NOT MATCHED THEN
                                                5 INSERT
                                                6 VALUES (np.product_id, np.product_name,
                                                7 np.category);
                                                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
2、带条件的Updates和Inserts子句

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:

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;
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:

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>
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:






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>
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.

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>
产品ID为1502的行从表PRODUCTS中被删除, 因为它同时匹配ON条件和DELETE WHERE条件. 产品ID为1501的行匹配DELETE WHERE条件但不匹配ON条件, 所以它没有被删除. 产品ID为1700 的行不匹配ON条件, 所以被插入表PRODUCTS. 产品ID为1601和1666的行匹配ON条件但不匹配DELETE WHERE条件, 所以被更新为表NEWPRODUCTS中的值.