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

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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 * fro