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oracle-merge用法詳解

編輯：Oracle數據庫基礎

Oracle9i引入了MERGE命令,你能夠在一個SQL語句中對一個表同時執行inserts和updates操作. MERGE命令從一個或多個數據源中選擇行來updating或inserting到一個或多個表.在Oracle 10g中MERGE有如下一些改進：

1、UPDATE或INSERT子句是可選的

2、UPDATE和INSERT子句可以加WHERE子句

3、在ON條件中使用常量過濾謂詞來insert所有的行到目標表中,不需要連接源表和目標表

4、UPDATE子句後面可以跟DELETE子句來去除一些不需要的行

首先創建示例表：

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語句要求你必須同時指定INSERT和UPDATE子句.而在Oracle 10g, 你可以省略UPDATE或INSERT子句中的一個. 下面的例子根據表NEWPRODUCTS的PRODUCT_ID字段是否匹配來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語句影響到是產品id為1502, 1601和1666的行. 它們的產品名字和種類被更新為表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, 對於在兩個表中能夠匹配上PRODUCT_ID的數據不作任何處理. 從這個例子你能看到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、帶條件的Updates和Inserts子句

你能夠添加WHERE子句到UPDATE或INSERT子句中去, 來跳過update或insert操作對某些行的處理. 下面例子根據表NEWPRODUCTS來更新表PRODUCTS數據, 但必須字段CATEGORY也得同時匹配上:

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 POTTERDVD
    SQL>
    SQL> rollback;

在這個例子中, 產品ID為1502,1601和1666匹配ON條件但是1666的category不匹配. 因此MERGE命令只更新兩行數據. 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>

注意由於有WHERE子句INSERT沒有插入所有不匹配ON條件的行到表PRODUCTS.

3、無條件的Inserts

你能夠不用連接源表和目標表就把源表的數據插入到目標表中. 這對於你想插入所有行到目標表時是非常有用的. Oracle 10g現在支持在ON條件中使用常量過濾謂詞. 舉個常量過濾謂詞例子ON (1=0). 下面例子從源表插入行到表PRODUCTS, 不檢查這些行是否在表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 se 

      lected.
    SQL>

4、新增加的DELETE子句

Oracle 10g中的MERGE提供了在執行數據操作時清除行的選項. 你能夠在WHEN MATCHED THEN UPDATE子句中包含DELETE子句. DELETE子句必須有一個WHERE條件來刪除匹配某些條件的行.匹配DELETE WHERE條件但不匹配ON條件的行不會被從表中刪除.

下面例子驗證DELETE子句. 我們從表NEWPRODUCTS中合並行到表PRODUCTS中, 但刪除category為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>

產品ID為1502的行從表PRODUCTS中被刪除, 因為它同時匹配ON條件和DELETE WHERE條件. 產品ID為1501的行匹配DELETE WHERE條件但不匹配ON條件, 所以它沒有被刪除. 產品ID為1700 的行不匹配ON條件, 所以被插入表PRODUCTS. 產品ID為1601和1666的行匹配ON條件但不匹配DELETE WHERE條件, 所以被更新為表NEWPRODUCTS中的值.