把數據從一個表復制到另一個表，插入新數據或替換掉老數據是每一個ORACLE DBA都會經常碰到的問題。在ORACLE9i以前的年代，我們要先查找是否存在老數據，如果有用UPDATE替換，否則用INSERT語句插入，其間少不了還有一些標記變量等等，繁瑣的很。現在ORACLE9i專為這種情況提供了MERGE語句，使這一工作變得異常輕松。MERGE語句的語法如下：

MERGE [hint] INTO [schema .] table [t_alias] USING [schema .] { table | view | subquery } [t_alias] ON ( condition ) WHEN MATCHED THEN merge_update_clause WHEN NOT MATCHED THEN merge_insert_clause; 例如： MERGE INTO tdest d USING tsrc s ON (s.srckey = d.destkey) WHEN MATCHED THEN UPDATE SET d.destdata = d.destdata + s.srcdata WHEN NOT MATCHED THEN INSERT (destkey,destdata) VALUES (srckey,srcdata) 一條語句代替了原來的一段復雜語句 在Oracle 10g中MERGE有如下一些改進：

?/P>

1、UPDATE或INSERT子句是可選的

?/P>

2、UPDATE和INSERT子句可以加WHERE子句

?/P>

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

?/P>

4、UPDATE子句后面可以跟DELETE子句來去除一些不需要的行

?/P>

首先創建示例表：

?/P>

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

?/P>

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:

?/P>

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>

?/P>

?/P>

?/P>

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, 對于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.

?/P>

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

?/P>

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:

?/P>

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;

?/P>

?/P>

?/P>

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:

?/P>

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>

?/P>

?/P>

注意由于有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

?/P>

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. 這對于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:

?/P>

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>

?/P>

?/P>

?/P>

4、新增加的DELETE子句

?/P>

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.

?/P>

下面例子驗證DELETE子句. 我們從表NEWPRODUCTS中合并行到表PRODUCTS中, 但刪除category為ELECTRNCS的行.

?/P>

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>

?/P>

?/P>

?/P>

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.

轉載于:https://www.cnblogs.com/weixun/archive/2013/04/15/3022962.html

總結

以上是生活随笔為你收集整理的merge语句的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。