Oracle merge into 命令
原文:http://jayklin.iteye.com/blog/1669114
作用:merge into 解决用B表跟新A表数据,如果A表中没有,则把B表的数据插入A表;当处理大数据量是,该方法的效率很高。
语法:
MERGE INTO [your table-name] [rename your table here]
USING ( [write your query here] )[rename your query-sql and using just like a table]
ON ([conditional expression here] AND [...]...)
WHEN MATHED THEN [here you can execute some update sql or something else ]
WHEN NOT MATHED THEN [execute something else here ! ]
copy:http://blog.csdn.net/nsj820/article/details/5755685
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Oracle10g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
语法:
MERGEHINTINTO SCHEMA .TABLE T_ALIAS
USINGSCHEMA . {TABLE | VIEW |SUBQUERY } T_ALIAS
ON (CONDITION)
WHENMATCHEDTHEN MERGE_UPDATE_CLAUSE
WHENNOTMATCHED THEN 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 plaincopyprint?
01.DROP TABLE PRODUCTS;
02.DROP TABLE NEWPRODUCTS;
03.create table PRODUCTS
04.(
05.PRODUCT_ID INTEGER,
06.PRODUCT_NAME VARCHAR2(60),
07.CATEGORY VARCHAR2(60)
08.);
09.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
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01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN MATCHED THEN
05. UPDATE
06. SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
07. P.CATEGORY = NP.CATEGORY;
08.
09.SELECT * FROM PRODUCTS;
10.SELECT * FROM NEWPRODUCTS;
3、不匹配插入
[c-sharp] view plaincopyprint?
01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN NOT MATCHED THEN
05. INSERT
06. (PRODUCT_ID
07. ,PRODUCT_NAME
08. ,CATEGORY)
09. VALUES
10. (NP.PRODUCT_ID
11. ,NP.PRODUCT_NAME
12. ,NP.CATEGORY);
13.
14.SELECT * FROM PRODUCTS;
15.SELECT * FROM NEWPRODUCTS;
4、匹配带where/on更新
[c-sharp] view plaincopyprint?
01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN MATCHED THEN
05. UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME WHERE P.CATEGORY = NP.CATEGORY;
06.
07.MERGE INTO PRODUCTS P
08.USING NEWPRODUCTS NP
09.ON (P.PRODUCT_ID = NP.PRODUCT_ID AND P.CATEGORY = NP.CATEGORY)
10.WHEN MATCHED THEN
11. UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME;
12.
13.SELECT * FROM PRODUCTS;
14.SELECT * FROM NEWPRODUCTS;
15.
16.SELECT *
17. FROM PRODUCTS A
18. INNER JOIN NEWPRODUCTS B
19. ON A.PRODUCT_ID = B.PRODUCT_ID
20. AND A.CATEGORY = B.CATEGORY;
5、匹配带where更新、插入
[c-sharp] view plaincopyprint?
01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN MATCHED THEN
05. UPDATE
06. SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
07. P.CATEGORY = NP.CATEGORY
08. WHERE P.CATEGORY = 'DVD'
09.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.
19.SELECT * FROM PRODUCTS;
20.SELECT * FROM NEWPRODUCTS;
6、ON常量表达式
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01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (1 = 0)
04.WHEN NOT MATCHED THEN
05. INSERT
06. (PRODUCT_ID
07. ,PRODUCT_NAME
08. ,CATEGORY)
09. VALUES
10. (NP.PRODUCT_ID
11. ,NP.PRODUCT_NAME
12. ,NP.CATEGORY) WHERE NP.CATEGORY = 'BOOKS';
13.
14.SELECT * FROM PRODUCTS;
15.SELECT * FROM NEWPRODUCTS;
7、匹配删除、不匹配插入
[c-sharp] view plaincopyprint?
01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN MATCHED THEN
05. UPDATE
06. SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
07. P.CATEGORY = NP.CATEGORY DELETE
08. WHERE (P.CATEGORY = 'ELECTRNCS')
09.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.
19.SELECT * FROM PRODUCTS;
20.SELECT * FROM NEWPRODUCTS;
8、源表为子查询(自联接)
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01.MERGE INTO PRODUCTS P
02.USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1501) B
03.ON (B.CO <> 0)
04.WHEN MATCHED THEN
05. UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1501
06.WHEN NOT MATCHED THEN
07. INSERT
08. (PRODUCT_ID
09. ,PRODUCT_NAME
10. ,CATEGORY)
11. VALUES
12. (1501
13. ,'KEBO'
14. ,'NBA');
15.
16.MERGE INTO PRODUCTS P
17.USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1508) B
18.ON (B.CO <> 0)
19.WHEN MATCHED THEN
20. UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1508
21.WHEN NOT MATCHED THEN
22. INSERT
23. (PRODUCT_ID
24. ,PRODUCT_NAME
25. ,CATEGORY)
26. VALUES
27. (1508
28. ,'KEBO'
29. ,'NBA');
30.
31.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。
缺少一个带delete语句选项的示例,暂为补上:
[sql] view plaincopyprint?
01.MERGE INTO PRODUCTS P
02.USING NEWPRODUCTS NP
03.ON (P.PRODUCT_ID = NP.PRODUCT_ID)
04.WHEN MATCHED THEN
05. UPDATE
06. SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY
07. --WHERE (P.CATEGORY = 'ELECTRNCS')
08. DELETE
09. WHERE (P.CATEGORY = 'ELECTRNCS')
10.WHEN NOT MATCHED THEN
11. INSERT
12. (PRODUCT_ID, PRODUCT_NAME, CATEGORY)
13. VALUES
14. (NP.PRODUCT_ID, NP.PRODUCT_NAME, NP.CATEGORY);
15.
16.SELECT * FROM PRODUCTS;
17.SELECT * FROM NEWPRODUCTS;
说明:DELETE语句删除的是满足matched关联on条件,同时也要是update更新内容的子集,否则不会删除任何内容。
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