Oracle Merge 语言使用

动机:

想在Oracle中用一条SQL语句直接进行Insert/Update的操作。

说明:

在进行SQL语句编写时,我们经常会遇到大量的同时进行Insert/Update的语句 ,也就是说当存在记录时,就更新(Update),不存在数据时,就插入(Insert)。

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insertsupdates操作. MERGE命令从一个或多个数据源中选择行来updatinginserting到一个或多个表.Oracle10gMERGE有如下一些改进

1UPDATEINSERT子句是可选的

2UPDATEINSERT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

4UPDATE子句后面可以跟DELETE子句来去除一些不需要的行

语法:

MERGEHINTINTOSCHEMA . TABLE T_ALIAS

USINGSCHEMA . {TABLE |VIEW |SUBQUERY } T_ALIAS

ON (CONDITION)

WHENMATCHEDTHEN MERGE_UPDATE_CLAUSE

WHENNOTMATCHEDTHEN MERGE_INSERT_CLAUSE / MERGE_DELETE_CLAUSE;

联想:
merge
into是特有的功能,相当于在 MSSQL中的

ifexists(...)

updatetable

else

Insertinto table.

mergeinto语法不仅没有if exists语法啰嗦,而且比if exists 还要高效很多,常用来在oracle之间同步数据库表。

例子:

1、 创建测试表及数据

[c-sharp] view plain copy print ?
  1. DROP TABLE PRODUCTS;
  2. DROP TABLE NEWPRODUCTS;
  3. create table PRODUCTS
  4. (
  5. PRODUCT_ID INTEGER,
  6. PRODUCT_NAME VARCHAR2(60),
  7. CATEGORY VARCHAR2(60)
  8. );
  9. insert into PRODUCTS values (1501, 'VIVITAR 35MM', 'ELECTRNCS');
  10. insert into PRODUCTS values (1502, 'OLYMPUS IS50', 'ELECTRNCS');
  11. insert into PRODUCTS values (1600, 'PLAY GYM', 'TOYS');
  12. insert into PRODUCTS values (1601, 'LAMAZE', 'TOYS');
  13. insert into PRODUCTS values (1666, 'HARRY POTTER', 'DVD');
  14. commit;
  15. create table NEWPRODUCTS
  16. (
  17. PRODUCT_ID INTEGER,
  18. PRODUCT_NAME VARCHAR2(60),
  19. CATEGORY VARCHAR2(60)
  20. );
  21. insert into NEWPRODUCTS values (1502, 'OLYMPUS CAMERA', 'ELECTRNCS');
  22. insert into NEWPRODUCTS values (1601, 'LAMAZE', 'TOYS');
  23. insert into NEWPRODUCTS values (1666, 'HARRY POTTER', 'TOYS');
  24. insert into NEWPRODUCTS values (1700, 'WAIT INTERFACE', 'BOOKS');
  25. commit;

2、 匹配更新

[c-sharp] view plain copy print ?
  1. 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. SELECT * FROM PRODUCTS;
  9. SELECT * FROM NEWPRODUCTS;

3、 不匹配插入

[c-sharp] view plain copy print ?
  1. MERGE INTO PRODUCTS P
  2. USING NEWPRODUCTS NP
  3. ON (P.PRODUCT_ID = NP.PRODUCT_ID)
  4. WHEN NOT MATCHED THEN
  5. INSERT
  6. (PRODUCT_ID
  7. ,PRODUCT_NAME
  8. ,CATEGORY)
  9. VALUES
  10. (NP.PRODUCT_ID
  11. ,NP.PRODUCT_NAME
  12. ,NP.CATEGORY);
  13. SELECT * FROM PRODUCTS;
  14. SELECT * FROM NEWPRODUCTS;

4、 匹配带where/on更新

[c-sharp] view plain copy print ?
  1. MERGE INTO PRODUCTS P
  2. USING NEWPRODUCTS NP
  3. ON (P.PRODUCT_ID = NP.PRODUCT_ID)
  4. WHEN MATCHED THEN
  5. UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME WHERE P.CATEGORY = NP.CATEGORY;
  6. MERGE INTO PRODUCTS P
  7. USING NEWPRODUCTS NP
  8. ON (P.PRODUCT_ID = NP.PRODUCT_ID AND P.CATEGORY = NP.CATEGORY)
  9. WHEN MATCHED THEN
  10. UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME;
  11. SELECT * FROM PRODUCTS;
  12. SELECT * FROM NEWPRODUCTS;
  13. SELECT *
  14. FROM PRODUCTS A
  15. INNER JOIN NEWPRODUCTS B
  16. ON A.PRODUCT_ID = B.PRODUCT_ID
  17. AND A.CATEGORY = B.CATEGORY;

5、 匹配带where更新、插入

[c-sharp] view plain copy print ?
  1. 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. (PRODUCT_ID
  12. ,PRODUCT_NAME
  13. ,CATEGORY)
  14. VALUES
  15. (NP.PRODUCT_ID
  16. ,NP.PRODUCT_NAME
  17. ,NP.CATEGORY) WHERE NP.CATEGORY != 'BOOKS';
  18. SELECT * FROM PRODUCTS;
  19. SELECT * FROM NEWPRODUCTS;

6、 ON常量表达式

[c-sharp] view plain copy print ?
  1. MERGE INTO PRODUCTS P
  2. USING NEWPRODUCTS NP
  3. ON (1 = 0)
  4. WHEN NOT MATCHED THEN
  5. INSERT
  6. (PRODUCT_ID
  7. ,PRODUCT_NAME
  8. ,CATEGORY)
  9. VALUES
  10. (NP.PRODUCT_ID
  11. ,NP.PRODUCT_NAME
  12. ,NP.CATEGORY) WHERE NP.CATEGORY = 'BOOKS';
  13. SELECT * FROM PRODUCTS;
  14. SELECT * FROM NEWPRODUCTS;

7、 匹配删除、不匹配插入

[c-sharp] view plain copy print ?
  1. 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 DELETE
  8. WHERE (P.CATEGORY = 'ELECTRNCS')
  9. WHEN NOT MATCHED THEN
  10. INSERT
  11. (PRODUCT_ID
  12. ,PRODUCT_NAME
  13. ,CATEGORY)
  14. VALUES
  15. (NP.PRODUCT_ID
  16. ,NP.PRODUCT_NAME
  17. ,NP.CATEGORY);
  18. SELECT * FROM PRODUCTS;
  19. SELECT * FROM NEWPRODUCTS;

8、 源表为子查询(自联接)

[c-sharp] view plain copy print ?
  1. MERGE INTO PRODUCTS P
  2. USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1501) B
  3. ON (B.CO <> 0)
  4. WHEN MATCHED THEN
  5. UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1501
  6. WHEN NOT MATCHED THEN
  7. INSERT
  8. (PRODUCT_ID
  9. ,PRODUCT_NAME
  10. ,CATEGORY)
  11. VALUES
  12. (1501
  13. ,'KEBO'
  14. ,'NBA');
  15. MERGE INTO PRODUCTS P
  16. USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1508) B
  17. ON (B.CO <> 0)
  18. WHEN MATCHED THEN
  19. UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1508
  20. WHEN NOT MATCHED THEN
  21. INSERT
  22. (PRODUCT_ID
  23. ,PRODUCT_NAME
  24. ,CATEGORY)
  25. VALUES
  26. (1508
  27. ,'KEBO'
  28. ,'NBA');
  29. SELECT * FROM PRODUCTS;

优点:

避免了分开更新

提高性能并易于使用

在数据仓库应用中十分有用

使用merge比传统的先判断再选择插入或更新快很多

需要注意的地方:

1、从语法条件上看(ON (join condition) ),merge into也是一个危险的语法。如果不慎重使用,会将源表全部覆盖到目标表,既危险又浪费效率,违背了增量同步的原则。所以在设计表结构时,一般每条记录都有更新时间的字段,用目标表最大更新时间判断源表数据是否有更新和新增的信息。

2、更新的字段,不允许有关联条件的字段(join condition)。比如条件是 A.ID=B.ID,那么使用SET A.ID=B.ID”将报出一个莫名其妙的提示错误。

http://www.cnblogs.com/highriver/archive/2011/08/02/2125043.html

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