[20190825]Join View and delete.txt

[20190825]Join View and delete.txt

--//看了链接https://jonathanlewis.wordpress.com/2019/08/20/join-view/,里面提到delete可能引起的错误,自己也测试看看.
--//顺便说一下,我自己也在维护中也喜欢这样方式,但是我从来不是多表连接操作.我一般操作单表.

1.环境:
SCOTT@test01p> @ ver1
PORT_STRING          VERSION    BANNER                                                                       CON_ID
-------------------- ---------- ---------------------------------------------------------------------------- ------
IBMPC/WIN_NT64-9.1.0 12.2.0.1.0 Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production      0

create table source
as
select level n1
from dual
connect by level <= 10
/

create table search
as
select level n1
from dual
connect by level <= 10
/

alter table source modify n1 not null;
alter table search modify n1 not null;

create unique index search_idx on search(n1);
-- create unique index source_idx on source(n1);
--//分析略.

2.测试1:
--//测试脚本如下:
$ cat jv1.txt
prompt  ===============================
prompt  Source referenced first in ANSI
prompt  ===============================
prompt delete from (select * from source s join search s1 on s.n1 = s1.n1);

delete from (select * from source s join search s1 on s.n1 = s1.n1);
select count(1) source_count from source;
select count(1) search_count from search;
rollback;

$cat jv2.txt
prompt  ===============================
prompt  Search referenced first in ANSI
prompt  ===============================
prompt delete from (select * from search s join source s1 on s.n1 = s1.n1);

delete from (select * from search s join source s1 on s.n1 = s1.n1);
select count(1) source_count from source;
select count(1) search_count from search;
rollback;

--//开始测试:
SCOTT@test01p> @ jv1.txt
===============================
Source referenced first in ANSI
===============================
delete from (select * from source s join search s1 on s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
           0
SEARCH_COUNT
------------
          10
Rollback complete.

SCOTT@test01p> @ jv2.txt
===============================
Search referenced first in ANSI
===============================
delete from (select * from search s join source s1 on s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
           0
SEARCH_COUNT
------------
          10
Rollback complete.

--//可以发现在这样情况下删除的表search.主要是表search有唯一索引.source没有索引.

3.测试2:
SCOTT@test01p> create unique index source_idx on source(n1);
Index created.

SCOTT@test01p> @ jv1.txt
===============================
Source referenced first in ANSI
===============================
delete from (select * from source s join search s1 on s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
           0
SEARCH_COUNT
------------
          10
Rollback complete.

SCOTT@test01p> @ jv2.txt
===============================
Search referenced first in ANSI
===============================
delete from (select * from search s join source s1 on s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
          10
SEARCH_COUNT
------------
           0
Rollback complete.

--//可以发现对source建立唯一索引后,脚本jv1.txt中删除的表source.
--//脚本jv2.txt中删除的表search.

4.测试3:
--//加入提示:
prompt  ============================================
prompt  Source hinted as leading table in join order
prompt  ============================================
prompt delete from ( select /*+ leading(s1, s) */ * from search s, source s1 where s.n1 = s1.n1) ;

delete from ( select /*+ leading(s1, s) */ * from search s, source s1 where s.n1 = s1.n1) ;
select count(1) source_count from source;
select count(1) search_count from search;
rollback;

prompt  ============================================
prompt  Search hinted as leading table in join order
prompt  ============================================
prompt delete from ( select /*+ leading(s, s1) */ * from search s, source s1 where s.n1 = s1.n1) ;

delete from ( select /*+ leading(s, s1) */ * from search s, source s1 where s.n1 = s1.n1) ;
select count(1) source_count from source;
select count(1) search_count from search;
rollback;

SCOTT@test01p> @ jv3.txt
============================================
Source hinted as leading table in join order
============================================
delete from ( select /*+ leading(s1, s) */ * from search s, source s1 where s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
          10
SEARCH_COUNT
------------
           0
Rollback complete.

============================================
Search hinted as leading table in join order
============================================
delete from ( select /*+ leading(s, s1) */ * from search s, source s1 where s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
          10
SEARCH_COUNT
------------
           0
Rollback complete.

--//我开始以为这样测试结果会不同,实际上这两个提示删除的都是表search.视乎是连接时那个表在前面dml操作的就是那个表.
--//总之这样连接操作要小心,我一般不这样写dml语句.

5.不过当我测试时还是无法理解一些细节:
$ cat jv4.txt
prompt  ===============================
prompt  Source referenced first in ANSI
prompt  ===============================
prompt delete from (select s1.* from source s join search s1 on s.n1 = s1.n1);

delete from (select s1.* from source s join search s1 on s.n1 = s1.n1);
select count(1) source_count from source;
select count(1) search_count from search;
rollback;

--//我仅仅提取的是search表(s1)内容,而实际上还是删除表source.视乎这样操作与提取字段无关.

SCOTT@test01p> @ jv4.txt
===============================
Source referenced first in ANSI
===============================
delete from (select s1.* from source s join search s1 on s.n1 = s1.n1)
10 rows deleted.
SOURCE_COUNT
------------
           0
SEARCH_COUNT
------------
          10
Rollback complete.
--//而实际上依旧还是操作的是表source.

6.看来以后这类操作要小心,我一般个人喜欢单表操作:
$ cat jv5.txt
prompt  ===============================
prompt  using exists and delete search
prompt  ===============================
prompt delete from (select s1.* from search s1 where exists ( select 1 from source s where s.n1 = s1.n1));

delete from (select s1.* from search s1 where exists ( select 1 from source s where s.n1 = s1.n1));
select count(1) source_count from source;
select count(1) search_count from search;
rollback;


prompt  ===============================
prompt  using exists and delete source
prompt  ===============================
prompt delete from (select s.* from source s where exists ( select 1 from search s1 where s.n1 = s1.n1));

delete from (select s.* from source s where exists ( select 1 from search s1 where s.n1 = s1.n1));
select count(1) source_count from source;
select count(1) search_count from search;
rollback;


SCOTT@test01p> @ jv5.txt
===============================
using exists and delete search
===============================
delete from (select s1.* from search s1 where exists ( select 1 from source s where s.n1 = s1.n1))
10 rows deleted.
SOURCE_COUNT
------------
          10
SEARCH_COUNT
------------
           0
Rollback complete.

===============================
using exists and delete source
===============================
delete from (select s.* from source s where exists ( select 1 from search s1 where s.n1 = s1.n1))
10 rows deleted.
SOURCE_COUNT
------------
           0
SEARCH_COUNT
------------
          10
Rollback complete.

--//这样就没有问题了.

来自 “ ITPUB博客 ” ，链接：http://blog.itpub.net/267265/viewspace-2655197/，如需转载，请注明出处，否则将追究法律责任。

转载于:http://blog.itpub.net/267265/viewspace-2655197/