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 - ProductionSQL>
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 thenupdate set a.areacode=b.areacodewhen NOT MATCHED theninsert(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 theninsert(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 thenupdate set a.areacode=b.areacodeConnected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as studySQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905310001 0            531905320001 1            532905330001 2            533SQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when MATCHED then4          update set a.areacode=b.areacode5     when NOT MATCHED then6          insert(msid,bill_month,areacode) 7          values(b.msid,'200702',b.areacode);DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905320001     200702      532       0.00905330001     200702      533       0.00905310001     200702      531       0.00SQL> insert into subs values(905340001,3,534);1 row insertedSQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905340001 3            534905310001 0            531905320001 1            532905330001 2            533SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when NOT MATCHED then4          insert(msid,bill_month,areacode) 5          values(b.msid,'200702',b.areacode);DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905320001     200702      532       0.00905330001     200702      533       0.00905310001     200702      531       0.00905340001     200702      534       0.00SQL> update subs set areacode=999;4 rows updatedSQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905340001 3            999905310001 0            999905320001 1            999905330001 2            999SQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905320001     200702      532       0.00905330001     200702      533       0.00905310001     200702      531       0.00905340001     200702      534       0.00SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when MATCHED then4          update set a.areacode=b.areacode;DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905320001     200702      999       0.00905330001     200702      999       0.00905310001     200702      999       0.00905340001     200702      999       0.00SQL> 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 thenupdate set a.areacode=b.areacodewhere b.ms_type=0when NOT MATCHED theninsert(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 theninsert(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 thenupdate set a.areacode=b.areacodewhere b.ms_type=0;Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as studySQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905310001 0            531905320001 1            532905330001 2            533SQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when MATCHED then4          update set a.areacode=b.areacode5          where b.ms_type=06     when NOT MATCHED then7          insert(msid,bill_month,areacode) 8          values(b.msid,'200702',b.areacode)9          where b.ms_type=0;DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905310001     200702      531       0.00SQL> insert into subs values(905360001,0,536);1 row insertedSQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905360001 0            536905310001 0            531905320001 1            532905330001 2            533SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when NOT MATCHED then4          insert(msid,bill_month,areacode) 5          values(b.msid,'200702',b.areacode)6          where b.ms_type=0;DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905310001     200702      531       0.00905360001     200702      536       0.00SQL> update subs set areacode=888 where ms_type=0;2 rows updatedSQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905360001 0            888905310001 0            888905320001 1            532905330001 2            533SQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905310001     200702      531       0.00905360001     200702      536       0.00SQL>
SQL> merge into acct a2       using subs b on (a.msid=b.msid)3     when MATCHED then4          update set a.areacode=b.areacode5          where b.ms_type=0;DoneSQL> select * from acct;MSID BILL_MONTH AREACODE        FEE
---------- ---------- -------- ----------905310001     200702      888       0.00905360001     200702      888       0.00SQL>
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 thenupdate set a.areacode=b.areacode        delete where (b.ms_type!=0);             SQL> select * from subs;MSID MS_TYPE AREACODE
---------- ------- --------905310001 0            531905320001 1            532905330001 2            533SQL> select * from acct;MSID MS_TYPE AREACODE
---------- ------- --------905310001 0            531905320001 1            532905330001 2            533SQL>
SQL>  merge into acct a2       using subs b on (a.msid=b.msid)3     when MATCHED then4          update set a.areacode=b.areacode5          delete where (b.ms_type!=0);DoneSQL> select * from acct;MSID MS_TYPE AREACODE
---------- ------- --------905310001 0            531SQL> 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