:Oracle 中对Merge语句的增强 和去重复新增
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 - 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！原文链接：http://tomszrp.itpub.net/post/11835/263865
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存储过程的实现新增去重复
tzxd@webora9> drop table t ;Table dropped.tzxd@webora9> create table t (t1 number(5),t2 varchar2(20));Table created.tzxd@webora9> create index idx_t_t1 on t(t1);Index created.tzxd@webora9> declare 2 v_dummy number(1); 3 begin 4 select count(*) into v_dummy from t where t1 = 1 for update; 5 if v_dummy = 1 then 6 dbms_output.put_line('value 1 of t1 is exists '); 7 else 8 insert into t values(1,'test'); 9 end if;10 end;11 /PL/SQL procedure successfully completed.tzxd@webora9> edWrote file aaa.sqldeclare v_dummy number(1);begin select count(*) into v_dummy from t where t1 = 1 for update; if v_dummy = 1 then dbms_output.put_line('value 1 of t1 is exists '); else insert into t values(1,'test'); end if;end;/ 1 declare 2 v_dummy number(1); 3 begin 4 select count(*) into v_dummy from t where t1 = 1 for update; 5 if v_dummy = 1 then 6 dbms_output.put_line('value 1 of t1 is exists '); 7 else 8 insert into t values(1,'test'); 9 end if;10* end;tzxd@webora9> /PL/SQL procedure successfully completed.tzxd@webora9> select * from t; T1 T2---------- -------------------- 1 test ?