使用MERGE语句，这里简单总结一下 （一个语句解决update 和 insert 功能）

 在数据仓库中的转换和装载过程中，经常会使用MERGE语句，这里简单总结一下。

 

MERGE语句是Oracle9i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。
下面看个具体的例子：
SQL> CREATE TABLE T AS SELECT ROWNUM ID, A.* FROM DBA_OBJECTS A;
表已创建。
SQL> CREATE TABLE T1 AS
2 SELECT ROWNUM ID, OWNER, TABLE_NAME, CAST('TABLE' AS VARCHAR2(100)) OBJECT_TYPE
3 FROM DBA_TABLES;
表已创建。
SQL> MERGE INTO T1 USING T
2 ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME AND T.OBJECT_TYPE = T1.OBJECT_TYPE)
3 WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
4 WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME, T.OBJECT_TYPE);
6165 行已合并。
SQL> SELECT ID, OWNER, OBJECT_NAME, OBJECT_TYPE FROM T
2 MINUS
3 SELECT * FROM T1;
未选定行
MERGE语法其实很简单，下面稍微修改一下例子。
SQL> DROP TABLE T;
表已丢弃。
SQL> DROP TABLE T1;
表已丢弃。
SQL> CREATE TABLE T AS SELECT ROWNUM ID, A.* FROM DBA_OBJECTS A;
表已创建。
SQL> CREATE TABLE T1 AS SELECT ROWNUM ID, OWNER, TABLE_NAME FROM DBA_TABLES;
表已创建。
SQL> MERGE INTO T1 USING T
2 ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME)
3 WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
4 WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME);
MERGE INTO T1 USING T
*
ERROR 位于第 1 行:
ORA-30926: 无法在源表中获得一组稳定的行
这个错误是使用MERGE最常见的错误，造成这个错误的原因是由于通过连接条件得到的T的记录不唯一。最简单的解决方法类似：
SQL> MERGE INTO T1
2 USING (SELECT OWNER, OBJECT_NAME, MAX(ID) ID FROM T GROUP BY OWNER, OBJECT_NAME) T
3 ON (T.OWNER = T1.OWNER AND T.OBJECT_NAME = T1.TABLE_NAME)
4 WHEN MATCHED THEN UPDATE SET T1.ID = T.ID
5 WHEN NOT MATCHED THEN INSERT VALUES (T.ID, T.OWNER, T.OBJECT_NAME);
5775 行已合并。
另外，MERGE语句的UPDATE不能修改用于连接的列，否则会报错，详细信息可以参考：http://blog.itpub.net/post/468/14844

===============================================================

ref: http://tomszrp.itpub.net/post/11835/263865

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 - ProdPL/SQL Release 10.2.0.1.0 - ProductionCORE    10.2.0.1.0      ProductionTNS for 32-bit Windows: Version 10.2.0.1.0 - ProductionNLSRTL 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 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 studySQL> select * from subs;      MSID MS_TYPE AREACODE---------- ------- -------- 905310001 0            531 905320001 1            532 905330001 2            533SQL> 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);DoneSQL> select * from acct;      MSID BILL_MONTH AREACODE        FEE---------- ---------- -------- ---------- 905320001     200702      532       0.00 905330001     200702      533       0.00 905310001     200702      531       0.00SQL> insert into subs values(905340001,3,534);1 row insertedSQL> select * from subs;      MSID MS_TYPE AREACODE---------- ------- -------- 905340001 3            534 905310001 0            531 905320001 1            532 905330001 2            533SQL> 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);DoneSQL> 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       0.00SQL> update subs set areacode=999;4 rows updatedSQL> select * from subs;      MSID MS_TYPE AREACODE---------- ------- -------- 905340001 3            999 905310001 0            999 905320001 1            999 905330001 2            999SQL> 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       0.00SQL> 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;DoneSQL> 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       0.00SQL> 　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 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 studySQL> select * from subs;      MSID MS_TYPE AREACODE---------- ------- -------- 905310001 0            531 905320001 1            532 905330001 2            533SQL> 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;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            536 905310001 0            531 905320001 1            532 905330001 2            533SQL> 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;DoneSQL> select * from acct;      MSID BILL_MONTH AREACODE        FEE---------- ---------- -------- ---------- 905310001     200702      531       0.00 905360001     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            888 905310001 0            888 905320001 1            532 905330001 2            533SQL> select * from acct;      MSID BILL_MONTH AREACODE        FEE---------- ---------- -------- ---------- 905310001     200702      531       0.00 905360001     200702      536       0.00SQL> 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;DoneSQL> select * from acct;      MSID BILL_MONTH AREACODE        FEE---------- ---------- -------- ---------- 905310001     200702      888       0.00 905360001     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 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            533SQL> select * from acct;      MSID MS_TYPE AREACODE---------- ------- -------- 905310001 0            531 905320001 1            532 905330001 2            533SQL> 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);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！

T1必须是oracle实际存在的表！

declare
--T1必须是oracle实际存在的表或视图！
--create table t (c1 number,c2 number);
--insert into t values (1,2);
type TYPE_REC_RESULT is record(
C1 number,
C2 number);
type TYPE_TAB_RESULT is table of TYPE_REC_RESULT index by binary_integer;
T1 TYPE_TAB_RESULT;
begin
merge into T1
using T
on (T1.C1 = T.C1)
when matched then
update
set T1.C2 = T.C2
when not matched then
insert
values
(T.C1, T.C2);
end;
/
PL/SQL: ORA-00942: 表或视图不存在