[20160429]建立Extended Statistics 和函数索引问题.txt
--11G支持相关数据的统计分析,比如如果两个字段存在相关性通过分析,能够得到更加良好的统计信息,以及生成好的执行计划.
--但是如果结合函数索引呢?通过一个简单的例子来说明:
--前次做的测试:
http://blog.itpub.net/267265/viewspace-2089119/
1.环境:
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
SCOTT@book> create table t (a number, b date);
Table created.
2.建立Extended Statistics:
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,trunc(b))') from dual;
select dbms_stats.create_extended_stats(user,'T','(a,trunc(b))') from dual
*
ERROR at line 1:
ORA-20001: Invalid Extension: Column group can contain only columns seperated by comma
--可以看出建立 Column group仅仅包含字段,使用,隔开.
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,b)') from dual;
DBMS_STATS.CREATE_EXTENDED_STATS(USER,'T','(A,B)')
--------------------------------------------------
SYS_STUNA$6DVXJXTP05EH56DTIR0X
SCOTT@book> exec dbms_stats.drop_extended_stats(user,'T','(a,b)') ;
PL/SQL procedure successfully completed.
--上次我通过建立索引来实现函数+字段的Extended Statistics ,如果仔细看前面的提示建立索引后建立了一个hidden以及虚拟列
--SYS_NC00003$,如果我先建立一个虚拟列应该也可以实现.测试:
--建立虚拟列:
SCOTT@book> alter table t add (c date generated always as (trunc(b)));
Table altered.
SCOTT@book> select owner,table_name,column_name,data_type,data_default,hidden_column,virtual_column from DBA_TAB_COLS where owner=user and table_name='T';
OWNER TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT HID VIR
------ ---------- -------------------- ---------- -------------------- --- ---
SCOTT T C DATE TRUNC("B") NO YES
SCOTT T B DATE NO NO
SCOTT T A NUMBER NO NO
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,trunc(b))') c40 from dual;
C40
----------------------------------------
SYS_STU021V7H9RNW$DK6GQ1ZFI5B#
--OK!不过明显跟以前定义的名字不一样.前面测试如下:
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,trunc(b))') from dual;
DBMS_STATS.CREATE_EXTENDED_STATS(USER,'T','(A,TRUNC(B))')
----------------------------------------------------------
SYS_STUE4B2X1G802ME0XHTBYWFY_Q
--SYS_STUE4B2X1G802ME0XHTBYWFY_Q 与 SYS_STU021V7H9RNW$DK6GQ1ZFI5B# 不同.
SCOTT@book> select owner,table_name,column_name,data_type,data_default,hidden_column,virtual_column from DBA_TAB_COLS where owner=user and table_name='T';
OWNER TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT HID VIR
------ ---------- ------------------------------ ---------- ---------------------------------------- --- ---
SCOTT T SYS_STU021V7H9RNW$DK6GQ1ZFI5B# NUMBER SYS_OP_COMBINED_HASH("A",TRUNC("B")) YES YES
SCOTT T C DATE TRUNC("B") NO YES
SCOTT T B DATE NO NO
SCOTT T A NUMBER NO NO
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,c)') c40 from dual;
select dbms_stats.create_extended_stats(user,'T','(a,c)') c40 from dual
*
ERROR at line 1:
ORA-20001: Error when processing extension - virtual column is referenced in a column expression
ORA-06512: at "SYS.DBMS_STATS", line 8676
ORA-06512: at "SYS.DBMS_STATS", line 33335
--可以看出实际上建立的(a,c)的Extended Statistics.
SCOTT@book> exec dbms_stats.drop_extended_stats(user,'T','(a,trunc(b))');
PL/SQL procedure successfully completed.
--而删除后如用如下建立Extended Statistics
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,c)') c40 from dual;
select dbms_stats.create_extended_stats(user,'T','(a,c)') c40 from dual
*
ERROR at line 1:
ORA-20001: Error when processing extension - virtual column is referenced in a column expression
ORA-06512: at "SYS.DBMS_STATS", line 8676
ORA-06512: at "SYS.DBMS_STATS", line 33335
--很明显不能包含virtual column.
SCOTT@book> alter table t drop column c;
Table altered.
SCOTT@book> create index if_t_ab on t(a,trunc(b));
Index created.
SCOTT@book> select owner,table_name,column_name,data_type,data_default,hidden_column,virtual_column from DBA_TAB_COLS where owner=user and table_name='T';
OWNER TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT HID VIR
------ ---------- ------------------------------ ---------- ---------------------------------------- --- ---
SCOTT T SYS_NC00003$ DATE TRUNC("B") YES YES
SCOTT T B DATE NO NO
SCOTT T A NUMBER NO NO
SCOTT@book> select dbms_stats.create_extended_stats(user,'T','(a,SYS_NC00003$)') c40 from dual;
select dbms_stats.create_extended_stats(user,'T','(a,SYS_NC00003$)') c40 from dual
*
ERROR at line 1:
ORA-20001: Error when processing extension - virtual column is referenced in a column expression
ORA-06512: at "SYS.DBMS_STATS", line 8676
ORA-06512: at "SYS.DBMS_STATS", line 33335
--一样不行.
