oracle merge into 实例
Merge into 详细介绍MERGE语句是 oracle 9i 新增的语法，用来合并 UPDATE 和 INSERT 语句。
通过MERGE语句，根据一张表或子查询的连接条件对另外一张表进行查询，
连接条件匹配上的进行UPDATE，无法匹配的执行INSERT。
这个语法仅需要一次全表扫描就完成了全部工作，执行效率要高于INSERT＋UPDATE。
drop table t;
CREATE TABLE T AS SELECT ROWNUM> drop table t1;
CREATE TABLE T1 AS
SELECT ROWNUM> MERGE INTO T1 USING T
ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME AND T.OBJECT_TYPE = T1.OBJECT_TYPE)
WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME, T.OBJECT_TYPE);
--insert后面不写表示插入全部列
MERGE INTO T1 USING T
ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME)
WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME, T.OBJECT_TYPE);
--常见错误，连接条件不能获得稳定的行，可以使用下面的用子查询
MERGE INTO T1
USING (SELECT OWNER, OBJECT_NAME, MAX(ID)> ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME)
WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME);
SELECT> MINUS
SELECT * FROM T1;
drop table subs;
create table subs(
msid number(9),
ms_type char(1),
areacode number(3)
);
drop table acct;
create table acct(
msid number(9),
bill_month number(6),
areacode number(3),
fee number(8,2) default 0.00
);
insert into subs values(905310001,0,531);
insert into subs values(905320001,1,532);
insert into subs values(905330001,2,533);
commit;
merge into acct a --操作的表
using subs b on (a.msid=b.msid) --使用原始数据来源的表，并且制定条件，条件必须有括号
when matched then
update set a.areacode=b.areacode
--当匹配的时候，执行update操作，和直接update的语法不一样，不需要制定表名
when not matched then
--当不匹配的时候，执行insert操作，也不需要制定表名，若指定字段插入，
--则在insert后用括号标明，不指定是全部插入
insert(msid,bill_month,areacode) values(b.msid,'200702',b.areacode);
--另外，MERGE语句的UPDATE不能修改用于连接的列，否则会报错
select * from acct;
select * from subs;
--10g新特性，单个操作
merge into acct a
using subs b on(a.msid=b.msid)
when not matched then
--只有单个not matched的时候，只做插入，不做更新，只有单个matched的时候，只做更新操作
insert(a.msid,a.bill_month,a.areacode) values(b.msid,'200702',b.areacode);
update acct set areacode=800 where msid=905320001;
delete from acct where areacode=533 or areacode=531;
insert into acct values(905320001,'200702',800,0.00);
--删除重复行
delete from subs b where b.rowid
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