MERGE用法详解
本文转自：http://blog.itpub.net/7204674/viewspace-468420/
分类： Linux
今天写程序的时候，遇到这样一个问题，假如存在记录则更新，不存在则插入。以前遇到这样的情况一般需要控制语句，游标来实现。偶然知道，MERGE语句，就可以实现Update和Insert的功能，特来实践一下。当然，首先来学习一下语法，看到oracle技术文档上是这样描述的：
语法：
merge::=
De.ion of merge.gif follows
merge_update_clause ::=
De.ion of merge_update_clause.gif follows
merge_insert_clause ::=
De.ion of merge_insert_clause.gif follows
where_clause::=
De.ion of where_clause.gif follows
INTO 字句
用于指定你所update或者Insert目的表。
USING Clause
用于指定你要update或者Insert的记录的来源，它可能是一个表，视图，子查询。
ON Clause
用于目的表和源表（视图，子查询）的关联，如果匹配（或存在），则更新，否则插入。
merge_update_clause
用于写update语句
merge_insert_clause
用于写insert语句
例子：
SQL> create table subs(msid number(9),
2 ms_type char(1),
3 areacode number(3)
4 );
表已创建
SQL> create table acct(msid number(9),
2 bill_month number(6),
3 areacode number(3),
4 fee number(8,2) default 0.00);
表已创建
SQL> insert into subs values(905310001,0,531);
已创建 1 行。
SQL> insert into subs values(905320001,1,532);
已创建 1 行。
SQL> insert into subs values(905330001,2,533);
已创建 1 行。
SQL> commit;
提交完成。
下面先演示一下merge的基本功能
1) matched 和not matched clauses 同时使用
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode);
2) 只有not matched clause,也就是只插入不更新
merge into acct a
using subs b on (a.msid=b.msid)
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode);
3) 只有matched clause, 也就是只更新不插入
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as study
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905310001 0 531
905320001 1 532
905330001 2 533
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when MATCHED then
4 update set a.areacode=b.areacode
5 when NOT MATCHED then
6 insert(msid,bill_month,areacode)
7 values(b.msid,'200702',b.areacode);
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905320001 200702 532 0.00
905330001 200702 533 0.00
905310001 200702 531 0.00
SQL> insert into subs values(905340001,3,534);
1 row inserted
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905340001 3 534
905310001 0 531
905320001 1 532
905330001 2 533
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when NOT MATCHED then
4 insert(msid,bill_month,areacode)
5 values(b.msid,'200702',b.areacode);
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905320001 200702 532 0.00
905330001 200702 533 0.00
905310001 200702 531 0.00
905340001 200702 534 0.00
SQL> update subs set areacode=999;
4 rows updated
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905340001 3 999
905310001 0 999
905320001 1 999
905330001 2 999
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905320001 200702 532 0.00
905330001 200702 533 0.00
905310001 200702 531 0.00
905340001 200702 534 0.00
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when MATCHED then
4 update set a.areacode=b.areacode;
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905320001 200702 999 0.00
905330001 200702 999 0.00
905310001 200702 999 0.00
905340001 200702 999 0.00
10g中增强一：条件操作
1) matched 和not matched clauses 同时使用
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
where b.ms_type=0
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode)
where b.ms_type=0;
2) 只有not matched clause,也就是只插入不更新
merge into acct a
using subs b on (a.msid=b.msid)
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode)
where b.ms_type=0;
3) 只有matched clause, 也就是只更新不插入
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
where b.ms_type=0;
Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as study
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905310001 0 531
905320001 1 532
905330001 2 533
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when MATCHED then
4 update set a.areacode=b.areacode
5 where b.ms_type=0
6 when NOT MATCHED then
7 insert(msid,bill_month,areacode)
8 values(b.msid,'200702',b.areacode)
9 where b.ms_type=0;
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905310001 200702 531 0.00
SQL> insert into subs values(905360001,0,536);
1 row inserted
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905360001 0 536
905310001 0 531
905320001 1 532
905330001 2 533
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when NOT MATCHED then
4 insert(msid,bill_month,areacode)
5 values(b.msid,'200702',b.areacode)
6 where b.ms_type=0;
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905310001 200702 531 0.00
905360001 200702 536 0.00
SQL> update subs set areacode=888 where ms_type=0;
2 rows updated
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905360001 0 888
905310001 0 888
905320001 1 532
905330001 2 533
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905310001 200702 531 0.00
905360001 200702 536 0.00
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when MATCHED then
4 update set a.areacode=b.areacode
5 where b.ms_type=0;
Done
SQL> select * from acct;
MSID BILL_MONTH AREACODE FEE
---------- ---------- -------- ----------
905310001 200702 888 0.00
905360001 200702 888 0.00
SQL>
10g中增强二：删除操作
An optional DELETE WHERE clause can be used to clean up after a
merge operation. Only those rows which match both the ON clause
and the DELETE WHERE clause are deleted.
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
delete where (b.ms_type!=0);
SQL> select * from subs;
MSID MS_TYPE AREACODE
---------- ------- --------
905310001 0 531
905320001 1 532
905330001 2 533
SQL> select * from acct;
MSID MS_TYPE AREACODE
---------- ------- --------
905310001 0 531
905320001 1 532
905330001 2 533
SQL>
SQL> merge into acct a
2 using subs b on (a.msid=b.msid)
3 when MATCHED then
4 update set a.areacode=b.areacode
5 delete where (b.ms_type!=0);
Done
SQL> select * from acct;
MSID MS_TYPE AREACODE
---------- ------- --------
905310001 0 531
说明：本文参考了oracle文档，例子是参考的http://xsb.itpub.net/post/419/30766。