MERGE INTO table_name alias1 USING (table|view|sub_query) alias2 ON (join condition) WHEN MATCHED THEN UPDATE table_name SET col1 = col_val1,col2 = col2_val WHEN NOT MATCHED THEN INSERT (column_list) VALUES (column_values) 关键字、参数 into子句 在into子句中指定所要修改或者插入数据的目标表 using子句 在using子句中指定用来修改或者插入的数据源。数据源可以是表、视图或者一个子查询语句。 on子句 在on子句中指定执行插入或者修改的满足条件。 when matched | not matched 用该子句通知 数据库如何对满足或不满足条件的结果做出相应的操作。可以使用以下的两类子句。
merge_update子句 merge_update子句执行对目标表中的字段值修改。当在符合on子句条件的情况下执行。如果修改子句执行,则目标表上的修改触发器将被触发。 merge_update子句 merge_update子句执行对目标表中的字段值修改。当在符合on子句条件的情况下执行。如果修改子句执行,则目标表上的修改触发器将被触发。
限制:当修改一个视图时,不能指定一个default值 merge_insert 子句 merge_insert子句执行当不符合on子句条件时,往目标表中插入数据。如果插入子句执行,则目标表上插入触发器将被触发。 限制:当修改一个视图时,不能指定一个default值
MERGE INTO BONUSES D USING (SELECT EMPLOYEE_ID, SALARY, DEPARTMENT_ID FROM EMPLOYEES WHERE DEPARTMENT_ID = 80) S ON (D.EMPLOYEE_ID = S.EMPLOYEE_ID) WHEN MATCHED THEN UPDATE SET D.BONUS = D.BONUS + S.SALARY*.01 WHEN NOT MATCHED THEN INSERT (D.EMPLOYEE_ID, D.BONUS) VALUES (S.EMPLOYEE_ID, S.SALARY*0.01); MERGE INTO XCMDTRANSFERSTATE AS T USING TABLE (VALUES(?,?,?,?,?,?)) T1(DATASNO,EXTERIORSYSTEM,STATUS,DATA_TIME,MARKFORDELETE,DATATRANSFERNO) ON (T.DATATRANSFERNO = T1.DATATRANSFERNO) WHEN MATCHED THEN update set T.DATASNO = T1.DATASNO,T.EXTERIORSYSTEM = T1.EXTERIORSYSTEM,T.STATUS = T1.STATUS,T.LASTUP_TIME = T1.DATA_TIME,T.MARKFORDELETE = T1.MARKFORDELETE WHEN NOT MATCHED THEN INSERT (DATASNO,EXTERIORSYSTEM,STATUS,CREATE_TIME,MARKFORDELETE,DATATRANSFERNO) VALUES (T1.DATASNO,T1.EXTERIORSYSTEM,T1.STATUS,T1.DATA_TIME,T1.MARKFORDELETE,T1.DATATRANSFERNO MERGE INTO EMPLOYE AS EM USING MANAGER AS MA ON EM.EMPLOYEID=MA.MANAGERID WHEN MATCHED AND EM.SALARY<MA.SALARY THEN UPDATE SET EM.SALARY=MA.SALARY WHEN MATCHED AND EM.SALARY>MA.SALARY THEN SIGNAL SQLSTATE '70001' SET MESSAGE_TEXT = 'EM.SALARY>MA.SALARY' WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY) ELSE IGNORE; -----
DB2 Merge 语句的作用非常强大,它可以将一个表中的数据合并到另一个表中,在合并的同时可以进行插入、删除、更新等操作。我们还是先来看个简单的例子吧,假设你定义了一个雇员表(employe),一个经理表(manager),如下所示:
---雇员表(EMPLOYE)
CREATE TABLE EMPLOYE (
EMPLOYEID INTEGER NOT NULL,---员工号
NAME VARCHAR(20) NOT NULL,---姓名
SALARY DOUBLE---薪水
);
INSERT INTO EMPLOYE (EMPLOYEID,NAME,SALARY) VALUES
(1,'张三',1000),
(2,'李四',2000),
(3,'王五',3000),
(4,'赵六',4000),
(5,'高七',5000);
--经理表(MANAGER)
CREATE TABLE MANAGER (
EMPLOYEID INTEGER NOT NULL,---经理号
NAME VARCHAR(20) NOT NULL,---姓名
SALARY DOUBLE---薪水
);
INSERT INTO MANAGER (MANAGERID,NAME,SALARY) VALUES
(3,'王五',5000),
(4,'赵六',6000);
经过一段时间,你发现这样的数据模型,或者说表结构设计简直就是一大败笔,经理和雇员都是员工嘛,为什么要设计两个表呢?发现错误后就需要改正,所以你决定,删除经理表(MANAGER)表,将MANAGER 表中的数据合并到EMPLOYE 表中,仔细分析发现,王五在两个表中都存在(可能是干的好升官了),而刘八在EMPLOYE 表中并不存在,现在,我们要求把EMPLOYE 表中不存在的MANAGER都插入到EMPLOYE 表中,存在的更新薪水。该怎么办呢?这个问题并不难,通常,我们可以分两步,如下所示:
--更新存在的
UPDATE EMPLOYE AS EM SET SALARY=(SELECT SALARY FROM MANAGER WHERE MANAGERID=EM.EMPLOYEID)
WHERE EMPLOYEID IN (
SELECT MANAGERID FROM MANAGER
);
---插入不存在的
INSERT INTO EMPLOYE (EMPLOYEID,NAME,SALARY)
SELECT MANAGERID,NAME,SALARY FROM MANAGER WHERE MANAGERID NOT IN (
SELECT EMPLOYEID FROM EMPLOYE
);
上面的处理是可以的,但是我们还可以有更简单的方法,就是用Merge语句,如下所示:
MERGE INTO EMPLOYE AS EM
USING MANAGER AS MA
ON EM.EMPLOYEID=MA.MANAGERID
WHEN MATCHED THEN UPDATE SET EM.SALARY=MA.SALARY
WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY);
在上面的处理中,我们用经理表(MANAGER)的薪水更新了雇员表(EMPLOYE)的薪水,假设现在要求,如果经理表(MANAGER)的薪水>雇员表(EMPLOYE)的薪水的时候更新,否则不更新,怎么办呢?如下:
-1
MERGE INTO EMPLOYE AS EM
USING MANAGER AS MA
ON EM.EMPLOYEID=MA.MANAGERID
WHEN MATCHED AND EM.SALARY<MA.SALARY THEN UPDATE SET EM.SALARY=MA.SALARY
WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY);
-2
USING MANAGER AS MA
ON EM.EMPLOYEID=MA.MANAGERID
WHEN MATCHED AND EM.SALARY<MA.SALARY THEN UPDATE SET EM.SALARY=MA.SALARY
WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY)
else ignore
不仔细的朋友可能没有看出上面两条语句的区别,哈哈,请仔细对比一下这两条语句。上面的语句中多了ELSE IGNORE语句,它的意思正如它英文的意思,其它情况忽略不处理。
如果你认为理论上应该不存在EM.SALARY>MA.SALARY的数据,如果有,说明有问题,你想抛个异常,怎么办?如下:
MERGE INTO EMPLOYE AS EM
USING MANAGER AS MA
ON EM.EMPLOYEID=MA.MANAGERID
WHEN MATCHED AND EM.SALARY<MA.SALARY THEN UPDATE SET EM.SALARY=MA.SALARY
WHEN MATCHED AND EM.SALARY>MA.SALARY THEN SIGNAL SQLSTATE '70001' SET MESSAGE_TEXT = 'EM.SALARY>MA.SALARY'
WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY)
ELSE IGNORE;
对于EM.SALARY>MA.SALARY的情况,如果你不想抛异常,而是删除EMPLOYE中的数据,怎么办?如下:
MERGE INTO EMPLOYE AS EM
USING MANAGER AS MA
ON EM.EMPLOYEID=MA.MANAGERID
WHEN MATCHED AND EM.SALARY<MA.SALARY THEN UPDATE SET EM.SALARY=MA.SALARY
WHEN MATCHED AND EM.SALARY>MA.SALARY THEN DELETE
WHEN NOT MATCHED THEN INSERT VALUES (MA.MANAGERID,MA.NAME,MA.SALARY)
ELSE IGNORE;