Any way to materialize with fast refresh this query?

Question

I have three tables, A, B, C
my query is:
select
from
A
inner join B on B.col=A.col
left join C on C.b_id=B.id and C.a_id=A.id
in essence, C is overriding a value from B in case it exists. I use this join often so I'd like to materialize it for performance reasons. The problem is, Mview requires traditional syntax (why is that??) which does not support joining C on two tables. Any way around this?
Thanks

Answer 1

Jernej Kase wrote:
The problem is, Mview requires traditional syntax (why is that??) which does not support joining C on two tables. Any way around this?Hi Jernej,
Your analysis is right. I don't know why MV's don't support ANSI join syntax, but I have encountered it before. Probably because when MV's where introduced, the ANSI join didn't exist in Oracle yet. But there is a way around this.
First, reproducing your situation:
SQL> create table a(id,col)
  2  as
  3  select 1, 'name 1' from dual union all
  4  select 2, 'name 2' from dual union all
  5  select 3, 'name 3' from dual
  6  /
Tabel is aangemaakt.
SQL> create table b (id,col)
  2  as
  3  select 1, 'name 1' from dual union all
  4  select 2, 'name 2' from dual union all
  5  select 3, 'name 3' from dual
  6  /
Tabel is aangemaakt.
SQL> create table c (a_id,b_id,col)
  2  as
  3  select 2, 2, 'name c2' from dual union all
  4  select 3, 3, 'name c3' from dual union all
  5  select 4, 4, 'name c4' from dual
  6  /
Tabel is aangemaakt.
SQL> alter table a add primary key (id)
  2  /
Tabel is gewijzigd.
SQL> alter table b add primary key (id)
  2  /
Tabel is gewijzigd.
SQL> alter table c add primary key (a_id,b_id)
  2  /
Tabel is gewijzigd.
SQL> select
  2  *
  3  from
  4  A
  5  inner join B on B.col=A.col
  6  left join C on C.b_id=B.id and C.a_id=A.id
  7  /
   ID COL       ID COL     A_ID  B_ID COL
    1 name 1     1 name 1
    2 name 2     2 name 2     2     2 name c2
    3 name 3     3 name 3     3     3 name c3
3 rijen zijn geselecteerd.
SQL> create materialized view log on a with rowid
  2  /
Gematerialiseerde viewlog is aangemaakt.
SQL> create materialized view log on b with rowid
  2  /
Gematerialiseerde viewlog is aangemaakt.
SQL> create materialized view log on c with rowid
  2  /
Gematerialiseerde viewlog is aangemaakt.
SQL> create materialized view abc_mv
  2    refresh fast on commit
  3  as
  4  select a.rowid a_rowid
  5       , b.rowid b_rowid
  6       , c.rowid c_rowid
  7       , a.id    a_id
  8       , b.id    b_id
  9       , a.col   a_col
10       , b.col   b_col
11       , c.col   c_col
12    from A
13         inner join B on B.col=A.col
14         left join C on C.b_id=B.id and C.a_id=A.id
15  /
       left join C on C.b_id=B.id and C.a_id=A.id
FOUT in regel 14:
.ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized viewTo circumvent this error message, the only option I see is to use nested MV's like this:
SQL> create materialized view ab_mv
  2    refresh fast on commit
  3  as
  4  select a.rowid a_rowid
  5       , b.rowid b_rowid
  6       , a.id    a_id
  7       , b.id    b_id
  8       , a.col   a_col
  9       , b.col   b_col
10    from a
11       , b
12   where a.col = b.col
13  /
Gematerialiseerde view is aangemaakt.
SQL> create materialized view log on ab_mv with rowid
  2  /
Gematerialiseerde viewlog is aangemaakt.
SQL> create materialized view abc_mv
  2    refresh fast on commit
  3  as
  4  select ab.rowid ab_rowid
  5       , c.rowid  c_rowid
  6       , ab.a_id  a_id
  7       , ab.b_id  b_id
  8       , ab.a_col a_col
  9       , ab.b_col b_col
10       , c.col    c_col
11    from ab_mv ab
12       , c
13   where ab.a_id = c.a_id (+)
14     and ab.b_id = c.b_id (+)
15  /
Gematerialiseerde view is aangemaakt.And to show that this works:
SQL> select * from abc_mv
  2  /
AB_ROWID           C_ROWID             A_ID  B_ID A_COL  B_COL  C_COL
AAGpZ4AAQAAAS2sAAA                        1     1 name 1 name 1
AAGpZ4AAQAAAS2sAAB AAGpZxAAQAAAMrUAAA     2     2 name 2 name 2 name c2
AAGpZ4AAQAAAS2sAAC AAGpZxAAQAAAMrUAAB     3     3 name 3 name 3 name c3
3 rijen zijn geselecteerd.
SQL> update c set col = 'name c9' where a_id = 2
  2  /
1 rij is bijgewerkt.
SQL> commit
  2  /
Commit is voltooid.
SQL> select * from abc_mv
  2  /
AB_ROWID           C_ROWID             A_ID  B_ID A_COL  B_COL  C_COL
AAGpZ4AAQAAAS2sAAA                        1     1 name 1 name 1
AAGpZ4AAQAAAS2sAAB AAGpZxAAQAAAMrUAAA     2     2 name 2 name 2 name c9
AAGpZ4AAQAAAS2sAAC AAGpZxAAQAAAMrUAAB     3     3 name 3 name 3 name c3
3 rijen zijn geselecteerd.
SQL> insert into c values (1, 1, 'bla')
  2  /
1 rij is aangemaakt.
SQL> commit
  2  /
Commit is voltooid.
SQL> select * from abc_mv
  2  /
AB_ROWID           C_ROWID             A_ID  B_ID A_COL  B_COL  C_COL
AAGpZ4AAQAAAS2sAAA AAGpZxAAQAAAMrVAAA     1     1 name 1 name 1 bla
AAGpZ4AAQAAAS2sAAB AAGpZxAAQAAAMrUAAA     2     2 name 2 name 2 name c9
AAGpZ4AAQAAAS2sAAC AAGpZxAAQAAAMrUAAB     3     3 name 3 name 3 name c3
3 rijen zijn geselecteerd.Regards,
Rob.