oracle数据库零碎---Oracle Merge 使用,表中存在数据就修改,没有数据自动添加

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

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DROP TABLE PRODUCTS;
DROP TABLE NEWPRODUCTS;
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;

DROP TABLE PRODUCTS;DROP TABLE NEWPRODUCTS;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;
2、匹配更新

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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN MATCHED THEN
UPDATE
SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
P.CATEGORY = NP.CATEGORY;
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY;SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;
3、不匹配插入

[c-sharp]
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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(NP.PRODUCT_ID
,NP.PRODUCT_NAME
,NP.CATEGORY);
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (NP.PRODUCT_ID ,NP.PRODUCT_NAME ,NP.CATEGORY);SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;
4、匹配带where/on更新

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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN MATCHED THEN
UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME WHERE P.CATEGORY = NP.CATEGORY;
MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID AND P.CATEGORY = NP.CATEGORY)
WHEN MATCHED THEN
UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME;
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;
SELECT *
FROM PRODUCTS A
INNER JOIN NEWPRODUCTS B
ON A.PRODUCT_ID = B.PRODUCT_ID
AND A.CATEGORY = B.CATEGORY;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME WHERE P.CATEGORY = NP.CATEGORY;MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID AND P.CATEGORY = NP.CATEGORY)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME;SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;SELECT * FROM PRODUCTS A INNER JOIN NEWPRODUCTS B ON A.PRODUCT_ID = B.PRODUCT_ID AND A.CATEGORY = B.CATEGORY;
5、匹配带where更新、插入

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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN MATCHED THEN
UPDATE
SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
P.CATEGORY = NP.CATEGORY
WHERE P.CATEGORY = 'DVD'
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(NP.PRODUCT_ID
,NP.PRODUCT_NAME
,NP.CATEGORY) WHERE NP.CATEGORY != 'BOOKS';
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY WHERE P.CATEGORY = 'DVD'WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (NP.PRODUCT_ID ,NP.PRODUCT_NAME ,NP.CATEGORY) WHERE NP.CATEGORY != 'BOOKS';SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;
6、ON常量表达式

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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (1 = 0)
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(NP.PRODUCT_ID
,NP.PRODUCT_NAME
,NP.CATEGORY) WHERE NP.CATEGORY = 'BOOKS';
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (1 = 0)WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (NP.PRODUCT_ID ,NP.PRODUCT_NAME ,NP.CATEGORY) WHERE NP.CATEGORY = 'BOOKS';SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;
7、匹配删除、不匹配插入

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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN MATCHED THEN
UPDATE
SET P.PRODUCT_NAME = NP.PRODUCT_NAME,
P.CATEGORY = NP.CATEGORY DELETE
WHERE (P.CATEGORY = 'ELECTRNCS')
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(NP.PRODUCT_ID
,NP.PRODUCT_NAME
,NP.CATEGORY);
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY DELETE WHERE (P.CATEGORY = 'ELECTRNCS')WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (NP.PRODUCT_ID ,NP.PRODUCT_NAME ,NP.CATEGORY);SELECT * FROM PRODUCTS;SELECT * FROM NEWPRODUCTS;
8、源表为子查询(自联接)

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MERGE INTO PRODUCTS P
USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1501) B
ON (B.CO <> 0)
WHEN MATCHED THEN
UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1501
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(1501
,'KEBO'
,'NBA');
MERGE INTO PRODUCTS P
USING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1508) B
ON (B.CO <> 0)
WHEN MATCHED THEN
UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1508
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID
,PRODUCT_NAME
,CATEGORY)
VALUES
(1508
,'KEBO'
,'NBA');
SELECT * FROM PRODUCTS;

MERGE INTO PRODUCTS PUSING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1501) BON (B.CO <> 0)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1501WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (1501 ,'KEBO' ,'NBA');MERGE INTO PRODUCTS PUSING (SELECT COUNT(*) CO FROM PRODUCTS WHERE PRODUCTS.PRODUCT_ID = 1508) BON (B.CO <> 0)WHEN MATCHED THEN UPDATE SET P.PRODUCT_NAME = 'KEBO' WHERE P.PRODUCT_ID = 1508WHEN NOT MATCHED THEN INSERT (PRODUCT_ID ,PRODUCT_NAME ,CATEGORY) VALUES (1508 ,'KEBO' ,'NBA');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[b]语句选项的示例，暂为补上：[/b]

[sql]
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MERGE INTO PRODUCTS P
USING NEWPRODUCTS NP
ON (P.PRODUCT_ID = NP.PRODUCT_ID)
WHEN MATCHED THEN
UPDATE
SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY
--WHERE (P.CATEGORY = 'ELECTRNCS')
DELETE
WHERE (P.CATEGORY = 'ELECTRNCS')
WHEN NOT MATCHED THEN
INSERT
(PRODUCT_ID, PRODUCT_NAME, CATEGORY)
VALUES
(NP.PRODUCT_ID, NP.PRODUCT_NAME, NP.CATEGORY);
SELECT * FROM PRODUCTS;
SELECT * FROM NEWPRODUCTS;

MERGE INTO PRODUCTS PUSING NEWPRODUCTS NPON (P.PRODUCT_ID = NP.PRODUCT_ID)WHEN MATCHED THEN  UPDATE     SET P.PRODUCT_NAME = NP.PRODUCT_NAME, P.CATEGORY = NP.CATEGORY   --WHERE (P.CATEGORY = 'ELECTRNCS')   DELETE    WHERE (P.CATEGORY = 'ELECTRNCS')WHEN NOT MATCHED THEN  INSERT    (PRODUCT_ID, PRODUCT_NAME, CATEGORY)  VALUES    (NP.PRODUCT_ID, NP.PRODUCT_NAME, NP.CATEGORY);SELECT * FROM PRODUCTS;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。