Hi,
I got the following info on MViews from metalink. It is very good info and
hope it is useful to you.
Best regards,
Problem Description
-------------------
You are trying to create a materialized view which refreshes
automatically
when the underlying table is updated.
However, the create command fails with an ora-12051 or an ora-12054.
The select statement that you are using could be any of the following:
==============================================
create materialized view log on emp
with rowid(empno, ename, job, mgr, hiredate, sal, comm, deptno)
including new values
/
=============================================
create materialized view mv_emp_1
build immediate refresh fast on commit
as
select deptno, sum(sal), count(sal)
from emp
group by deptno
/
from emp
*
ERROR at line 5:
ORA-12054: cannot set the ON COMMIT refresh attribute for the
materialized view
=============================================
or
=============================================
create materialized view mv_emp_1
build immediate refresh fast on commit
as
select deptno, sum(sal)
from emp
group by deptno
/
=============================================
from emp
*
ERROR at line 5:
ORA-12054: cannot set the ON COMMIT refresh attribute for the
materialized view
Solution Description
--------------------
The correct script for creation of this materialized view is as follows:
==============================================
create materialized view log on emp
with rowid(empno, ename, job, mgr, hiredate, sal, comm, deptno)
including new values
/
================================================
create materialized view mv_emp_1
build immediate refresh fast on commit
as
select count(*), deptno, sum(sal), count(sal)
from emp
group by deptno
/
================================================
Explanation
-----------
One of the mandatory requirements for creation of an on-commit
materialized
view has not been satisfied.
ON-COMMIT :
Refresh occurs automatically when a transaction that modified one of the
materialized view's fact tables commits.
Can be used with materialized views on single table aggregates
and with materialized views containing joins only.
As can be seen from above, an ON-COMMIT can be used only under specific
cases:
These are:
1. The M.V. should have a single table aggregate or
2. the M.V. should have a join only.
3. count(*) must be present for Single-Table Aggregates (see example
above).
4. count(<col>) should be present.
Here, <col> stands for the column which is being aggregated.
Note: the only time that count(col)is not required is when
the aggregate itself is a count(col).
5. It should be possible perform a fast refresh on the materialized view.
Fast refresh by itself has a few restrictions.
These are as follows:
a)The FROM list must contain base tables only (that is, no views).
b)It cannot contain references to non-repeating expressions like
SYSDATE and ROWNUM.
c)It cannot contain references to RAW or LONG RAW data types.
d)It cannot contain HAVING or CONNECT BY clauses.
e)The WHERE clause can contain only joins and they must be
equi-joins
(inner or outer) and all join predicates must be connected with
ANDs. No selection predicates on individual tables are allowed
f)It cannot have subqueries, inline views, or set functions like
UNION or MINUS.
In addition for M.V.'s with Single-Table Aggregates and Materialized
Views
with Joins and Aggregates, there are some more conditions on refresh
to the ones mentioned above:
Single Table Aggregates:
=======================
i) They can only have a single table.
ii) The SELECT list must contain all GROUP BY columns.
iii) Expressions are allowed in the GROUP BY and SELECT
clauses provided they are the same.
iv) They cannot have a WHERE clause.
v) They cannot have a MIN or MAX function.
vi) A materialized view log must exist on the table and must
contain all
columns referenced in the materialized view. The log must
have been
created with the INCLUDING NEW VALUES clause.
vii) If AVG(expr) or SUM(expr) is specified, you must have
COUNT(expr).
viii) If VARIANCE(expr) or STDDEV(expr) is specified,
you must have COUNT(expr) and SUM(expr).
Joins and Aggregates :
=====================
i)The WHERE clause can contain inner equi-joins only
(that is, no outer joins)
ii)Materialized views from this category are FAST refreshable after
Direct Load to the base tables; they are not FAST refreshable
after
conventional DML to the base tables.
iii)Materialized views from this category can have only the
ON DEMAND option (so, the on-commit cannot be used for this
category).
References
----------
Oracle8i Data Warehousing Guide : A76994-01
[BUG:888784]
.
"Reddy, Madhusudana"
<Madhusudana.Reddy@be To: Multiple recipients of list
ORACLE-L <[EMAIL PROTECTED]>
stbuy.com> cc:
Sent by: Subject: Suggestions on MV
Implementation !!!!!!!
[EMAIL PROTECTED]
06/21/2002 02:58 PM
Please respond to
ORACLE-L
Hello All,
I have a set of Materialized views in my DB . we refresh ( COMPLETE) these
MVs, couple of times a day. Web server ( application ) will hit these MVs
to
show the data on web pages. But the complete Refresh of MVs are consuming
much time and , at this point of time , Application is not able to show
right data on web pages. This is like a down time. I need some suggestions
from you all, in order to minimize or zeroing this down time.
The first thing I can think of is , FAST refresh , but one of my Sr.DBA
told
me that the MV definition will not allow us for a FAST refresh( Are there
any limitations for FAST refresh ???? ). Here is a sample MV Definition :
CREATE MATERIALIZED VIEW GENRELOB
NOLOGGING
BUILD IMMEDIATE
REFRESH COMPLETE ON DEMAND
DISABLE QUERY REWRITE
AS SELECT DISTINCT
'1' AS CLIP,
LOB.LOB_ID,
LOB.LOB_CD,
GENRE.GENRE_ID,
GENRE.GENRE_DESC,
GENRE.GENRE_DESC AS INSTANCENAME
FROM
GENRE,
GENRE_LOB_XREF,
LOB,
GENRE_PRODUCT_XREF
WHERE
GENRE.GENRE_ID = GENRE_LOB_XREF.GENRE_ID AND
GENRE_LOB_XREF.LOB_ID = LOB.LOB_ID AND
GENRE_PRODUCT_XREF.genre_id = GENRE.genre_id AND
GENRE.DSPLY_IND = 'Y'
ORDER BY
LOB_CD,
GENRE_DESC
;
My Goal is to view the FRESH data on web pages all the time , irrespective
of MV Refresh. Would anybody suggest me some bright ideas , to have no or
less down time ???
Thanks in advance
Madhu V Reddy
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