Question

Lets say I have two tables, tab_a and tab_b.

And I create a view like the following:

create view join_tabs as
(
  select col_x as col_z from tab_a
  union
  select col_y as col_z from tab_b
);

And if I do the following:

select * from join_tabs where col_z = 'BLAH';

If tab_a indexes col_x and tab_b indexes col_y, we should be able to do this with two index searches.

However, it would be nice if I could make an index over both tables in one index, or even index the view, in a way that automatically updates immediately if the source tables (tab_a or tab_b) change.

Is there a way to do this in Oracle?

Answer 1

I’m not up-to-par with Oracle but I believe Materialized Views do exactly that.

Choosing Indexes for Materialized Views

The two most common operations on a
materialized view are query execution
and fast refresh, and each operation
has different performance
requirements. Query execution might
need to access any subset of the
materialized view key columns, and
might need to join and aggregate over
a subset of those columns.
Consequently, query execution usually
performs best if a single-column
bitmap index is defined on each
materialized view key column.

In the case of materialized views
containing only joins using fast
refresh, Oracle recommends that
indexes be created on the columns that
contain the rowids to improve the
performance of the refresh operation.

If a materialized view using
aggregates is fast refreshable, then
an index is automatically created
unless USING NO INDEX is specified in
the CREATE MATERIALIZED VIEW
statement.