本文详细介绍了Oracle10g中MERGE语句的使用方法，包括基本功能如匹配更新和不匹配插入，以及10g版本新增的条件选项和DELETE操作，并通过具体示例进行说明。
在Oracle 10g之前，merge语句支持匹配更新和不匹配插入2种简单的用法，在10g中Oracle对merge语句做了增强，增加了条件选项和DELETE操作。下面我通过一个demo来简单介绍一下10g中merge的增强和10g前merge的用法。
参考Oracle 的SQL Reference，大家可以看到Merge Statement的语法如下：
MERGE [hint] INTO [schema .] table [t_alias] USING [schema .]
{ table | view | subquery } [t_alias] ON ( condition )
WHEN MATCHED THEN merge_update_clause
WHEN NOT MATCHED THEN merge_insert_clause;
下面我在windows xp 下10.2.0.1版本上做一个测试看看
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
SQL>
一、创建测试用的表
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>
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。
SQL>
二、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
SQL>
三、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>
四、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
SQL>
更为详尽的语法，请参考Oracle SQL Reference手册！
原文链接：http://tomszrp.itpub.net/post/11835/263865
存储过程的实现新增去重复
tzxd@webora9> drop table t ;
Table dropped.
tzxd@webora9> create table t (t1 number(5),t2 varchar2(20));
Table created.
tzxd@webora9> create index idx_t_t1 on t(t1);
Index created.
tzxd@webora9> declare
2 v_dummy number(1);
3 begin
4 select count(*) into v_dummy from t where t1 = 1 for update;
5 if v_dummy = 1 then
6 dbms_output.put_line('value 1 of t1 is exists ');
7 else
8 insert into t values(1,'test');
9 end if;
10 end;
11 /
PL/SQL procedure successfully completed.
tzxd@webora9> ed
Wrote file aaa.sql
declare
v_dummy number(1);
begin
select count(*) into v_dummy from t where t1 = 1 for update;
if v_dummy = 1 then
dbms_output.put_line('value 1 of t1 is exists ');
else
insert into t values(1,'test');
end if;
end;
/
1 declare
2 v_dummy number(1);
3 begin
4 select count(*) into v_dummy from t where t1 = 1 for update;
5 if v_dummy = 1 then
6 dbms_output.put_line('value 1 of t1 is exists ');
7 else
8 insert into t values(1,'test');
9 end if;
10* end;
tzxd@webora9> /
PL/SQL procedure successfully completed.
tzxd@webora9> select * from t;
T1 T2
---------- --------------------
1 test
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