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oracle的merge 函数使用 - asoka

更新时间: 2015-05-04 00:00:00 责任编辑: Author_N17

 

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 - 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!


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