ORACLE : Materialized view not working when Using LEFT JOIN

Question

I want to create a MATERIALIZED VIEW from a LEFT JOIN of 2 tables. However the following gives me an error:

    SELECT field1 
     FROM table_1 a 
     LEFT JOIN table_2 b 
     ON a.field1=b.field2

ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

However the following works:

SELECT field1 
 FROM table_1 a, table_2 b 
 WHERE a.field1=b.field2

Does anyone have any ideas why this is happening.

Thx for the help

Answer 1

• Run $ORACLE_HOME/admin/utlxmv.sql under your schema.

• Execute:

  DBMS_MVIEW.EXPLAIN_MVIEW('
  SELECT  field1 
  FROM    table_1 a
  LEFT JOIN
          table_2 b 
  ON      a.field1 = b.field2
  ');
  

• Run:

  SELECT  *
  FROM    mv_capabilities_table
  

and post the output here.

Answer 2

Followed the following instructions to make DBMS_MVIEW.EXPLAIN_MVIEW work: http://www.sqlsnippets.com/en/topic-12884.html

Capable of:

REFRESH_COMPLETE

Not Capable of:

REFRESH_FAST

REFRESH_FAST_AFTER_INSERT
inline view or subquery in FROM list not supported for this type MV

REFRESH_FAST_AFTER_INSERT
inline view or subquery in FROM list not supported for this type MV

REFRESH_FAST_AFTER_INSERT
view or subquery in from list

REFRESH_FAST_AFTER_ONETAB_DML
see the reason why REFRESH_FAST_AFTER_INSERT is disabled

MV_REPORT

REFRESH_FAST_AFTER_ANY_DML
see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled

Answer 3

There are two conditions that are not satisfied to make that materialized view refresh fast. First one is that you did not specify the rowid columns of every table involved. And the second one is an undocumented restriction: ANSI-joins are not supported.

Here is an example with DEPT being table_1, alias a and EMP being table_2, alias b:

SQL> create materialized view log on emp with rowid
  2  /

Materialized view log created.

SQL> create materialized view log on dept with rowid
  2  /

Materialized view log created.

SQL> create materialized view empdept_mv
  2    refresh fast on commit
  3  as
  4  select a.deptno
  5    from dept a
  6         left join emp b on (a.deptno = b.deptno)
  7  /
  from dept a
       *
ERROR at line 5:
ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

That mimics your situation. First add the rowid's:

SQL> create materialized view empdept_mv
  2    refresh fast on commit
  3  as
  4  select a.rowid dept_rowid
  5       , b.rowid emp_rowid
  6       , a.deptno
  7    from dept a
  8         left join emp b on (a.deptno = b.deptno)
  9  /
  from dept a
       *
ERROR at line 7:
ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

Still it cannot fast refresh, because of the ANSI joins. Converting to old-style outer join syntax:

SQL> create materialized view empdept_mv
  2    refresh fast on commit
  3  as
  4  select a.rowid dept_rowid
  5       , b.rowid emp_rowid
  6       , a.deptno
  7    from dept a
  8       , emp b
  9   where a.deptno = b.deptno (+)
 10  /

Materialized view created.

And to prove that it works:

SQL> select * from empdept_mv
  2  /

DEPT_ROWID         EMP_ROWID              DEPTNO
------------------ ------------------ ----------
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAA         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAB         30
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAC         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAD         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAE         30
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAF         30
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAG         10
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAH         20
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAI         10
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAJ         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAK         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAL         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAM         20
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAN         10
AAARhmAAEAAAAI/AAD                            40

15 rows selected.

SQL> insert into dept values (50,'IT','UTRECHT')
  2  /

1 row created.

SQL> commit
  2  /

Commit complete.

SQL> select * from empdept_mv
  2  /

DEPT_ROWID         EMP_ROWID              DEPTNO
------------------ ------------------ ----------
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAA         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAB         30
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAC         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAD         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAE         30
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAF         30
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAG         10
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAH         20
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAI         10
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAJ         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAK         20
AAARhmAAEAAAAI/AAC AAARhlAAEAAAAI3AAL         30
AAARhmAAEAAAAI/AAB AAARhlAAEAAAAI3AAM         20
AAARhmAAEAAAAI/AAA AAARhlAAEAAAAI3AAN         10
AAARhmAAEAAAAI/AAD                            40
AAARhmAAEAAAAI7AAA                            50

16 rows selected.

The ANSI-join syntax restriction is mentioned in point 6 in this blogpost.

Regards, Rob.