Subquery is not supported on fast refresh ?

Question

Hi ,
There is a long and complex sql statement in our production environment and the following subquery in it is called more 5 times in different clause.
I created materialized view to simplize it and decrease i/o, but fast refresh at commit time of the transaction was not support.
select report_dp as rpt_dp
from sys_currency_tbl where curr_cd = (select para_value from sys_system_param_tbl where para = 'base_currency')
SQL> select * from v$version;
BANNER
Oracle Database 10g Release 10.2.0.3.0 - 64bit Production
PL/SQL Release 10.2.0.3.0 - Production
CORE 10.2.0.3.0 Production
TNS for Linux: Version 10.2.0.3.0 - Production
NLSRTL Version 10.2.0.3.0 - Production
SQL> create materialized view log on sys_system_param_tbl tablespace tbs_tmp with rowid,sequence (para,para_value) including new values;
Materialized view log created.
SQL> create materialized view log on sys_currency_tbl tablespace tbs_tmp with rowid,sequence (report_dp,curr_cd) including new values;
Materialized view log created.
SQL> create materialized view sys_currency_tbl_mv
2 refresh fast
3 on commit
4 as
5 select report_dp as rpt_dp
6 from sys_currency_tbl where curr_cd = (select para_value from sys_system_param_tbl where para = 'base_currency');
FROM sys_currency_tbl WHERE curr_cd = (SELECT para_value FROM sys_system_param_tbl WHERE para = 'BASE_CURRENCY')
ERROR at line 6:
ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view
SQL> delete from mv_capabilities_table;
0 rows deleted.
SQL> exec dbms_mview.explain_mview('select report_dp as rpt_dp from sys_currency_tbl where curr_cd =
(select para_value from sys_system_param_tbl where para = ''base_currency'')','test');
PL/SQL procedure successfully completed.
SQL> set linesize 160
SQL> col msgtxt format a60
SQL> SELECT capability_name, possible,msgno,SUBSTR(msgtxt,1,60) AS msgtxt
2 FROM mv_capabilities_table
WHERE statement_id='test' and capability_name like '%FAST%';
3
CAPABILITY_NAME P MSGNO MSGTXT
REFRESH_FAST N
REFRESH_FAST_AFTER_INSERT N *2129 join or filter condition(s) are complex*
REFRESH_FAST_AFTER_ONETAB_DML N 2146 see the reason why REFRESH_FAST_AFTER_INSERT is disabled
REFRESH_FAST_AFTER_ANY_DML N 2161 see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled
REFRESH_FAST_PCT N 2157 PCT is not possible on any of the detail tables in the mater
General Restrictions on Fast Refresh
The defining query of the materialized view is restricted as follows:
     The materialized view must not contain references to non-repeating expressions like SYSDATE and ROWNUM.
     The materialized view must not contain references to RAW or LONG RAW data types.
     It cannot contain a SELECT list subquery.
     It cannot contain analytical functions (for example, RANK) in the SELECT clause.
     It cannot contain a MODEL clause.
     It cannot contain a HAVING clause with a subquery.
     It cannot contain nested queries that have ANY, ALL, or NOT EXISTS.
     It cannot contain a [START WITH …] CONNECT BY clause.
     It cannot contain multiple detail tables at different sites.
     On-commit materialized view cannot have remote detail tables.
     Nested materialized views must have a join or aggregate.
Above general restriction tell us subquery is not support on fast refresh, is right ?
If so could someone tell me how to simple the sql statement to avoid a lot of parse and I/O cost?

Answer 1

One way to simplify the statement and be able to use fast refreshed materialized views is getting rid of the sub-query
select a.reort_dp as rpt_dp
from sys_currency_tbl a ,  sys_system_param_tbl b
where a.curr_cd =b.para_value
and  b.para = 'base_currency'To get a faster execution, you need to do a comprehensive review of the statement, starting with explain plan, index availability and table/index statistics.
Iordan Iotzov
http://iiotzov.wordpress.com/