24/05/2005 14:37 FP 在數(shù)據(jù)倉(cāng)庫(kù)中的轉(zhuǎn)換和裝載過(guò)程中，經(jīng)常會(huì)使用MERGE語(yǔ)句，這里簡(jiǎn)單總結(jié)一下。
MERGE語(yǔ)句是Oracle9i新增的語(yǔ)法，用來(lái)合并UPDATE和INSERT語(yǔ)句。通過(guò)MERGE語(yǔ)句，根據(jù)一張表或子查詢的連接條件對(duì)另外一張表進(jìn)行查詢，連接條件匹配上的進(jìn)行UPDATE，無(wú)法匹配的執(zhí)行INSERT。這個(gè)語(yǔ)法僅需要一次全表掃描就完成了全部工作，執(zhí)行效率要高于INSERT＋UPDATE。
下面看個(gè)具體的例子：
SQL> CREATE TABLE T AS SELECT ROWNUM ID, A.* FROM DBA_OBJECTS A;
表已創(chuàng)建。
SQL> CREATE TABLE T1 AS
2 SELECT ROWNUM ID, OWNER, TABLE_NAME, CAST('TABLE' AS VARCHAR2(100)) OBJECT_TYPE
3 FROM DBA_TABLES;
表已創(chuàng)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;
未選定行
MERGE語(yǔ)法其實(shí)很簡(jiǎn)單，下面稍微修改一下例子。
SQL> DROP TABLE T;
表已丟棄。
SQL> DROP TABLE T1;
表已丟棄。
SQL> CREATE TABLE T AS SELECT ROWNUM ID, A.* FROM DBA_OBJECTS A;
表已創(chuàng)建。
SQL> CREATE TABLE T1 AS SELECT ROWNUM ID, OWNER, TABLE_NAME FROM DBA_TABLES;
表已創(chuàng)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: 無(wú)法在源表中獲得一組穩(wěn)定的行
這個(gè)錯(cuò)誤是使用MERGE最常見的錯(cuò)誤，造成這個(gè)錯(cuò)誤的原因是由于通過(guò)連接條件得到的T的記錄不唯一。最簡(jiǎn)單的解決方法類似：
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語(yǔ)句的UPDATE不能修改用于連接的列，否則會(huì)報(bào)錯(cuò)，詳細(xì)信息可以參考：http://blog.itpub.net/post/468/14844
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ref: http://tomszrp.itpub.net/post/11835/263865
在Oracle 10g之前，merge語(yǔ)句支持匹配更新和不匹配插入2種簡(jiǎn)單的用法，在10g中Oracle對(duì)merge語(yǔ)句做了增強(qiáng)，增加了條件選項(xiàng)和DELETE操作。下面我通過(guò)一個(gè)demo來(lái)簡(jiǎn)單介紹一下10g中merge的增強(qiáng)和10g前merge的用法。
參考Oracle 的SQL Reference，大家可以看到Merge Statement的語(yǔ)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版本上做一個(gè)測(cè)試看看
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、創(chuàng)建測(cè)試用的表
SQL> create table subs(msid number(9),
2 ms_type char(1),
3 areacode number(3)
4 );
表已創(chuàng)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);
表已創(chuàng)建。
SQL>
SQL> insert into subs values(905310001,0,531);
已創(chuàng)建 1 行。
SQL> insert into subs values(905320001,1,532);
已創(chuàng)建 1 行。
SQL> insert into subs values(905330001,2,533);
已創(chuàng)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 同時(shí)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中增強(qiáng)一：條件操作
1) matched 和not matched clauses 同時(shí)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中增強(qiáng)二：刪除操作
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>
更為詳盡的語(yǔ)法，請(qǐng)參考Oracle SQL Reference手冊(cè)！