How to create a materialized view with query rewrite enabled

In this example, I am creating a materialized view to support queries against a table with 20 million rows, which are looking at the maximum sequence number within a range of dates.

Oracle describes the benefits of Materialized views like this:

"One of the major benefits of creating and maintaining materialized views is the ability to take advantage of query rewrite, which transforms a SQL statement expressed in terms of tables or views into a statement accessing one or more materialized views that are defined on the detail tables."

Since I want the materialized view to be refreshed every time a new row is commited to the base table, I need to specify that the mview should use "fast refresh".

First, create a materialized view log to store changed rows in the base tables that your materialized views are built on. This is required when using FAST REFRESH:

CREATE MATERIALIZED VIEW LOG ON DATE_TO_SEQNO
TABLESPACE DATA1
CACHE
ENABLE ROW MOVEMENT
WITH ROWID (SEQNO, RDATE)
INCLUDING NEW VALUES;

Then, create the materialized view. Query rewrites are disabled by default, so it must be explicitly stated:

CREATE MATERIALIZED VIEW SEQ_AGGR_INFO
SEGMENT CREATION IMMEDIATE
TABLESPACE DATA1
CACHE
ENABLE ROW MOVEMENT
ROW STORE COMPRESS ADVANCED
BUILD IMMEDIATE
REFRESH FAST ON COMMIT
ENABLE QUERY REWRITE
AS
select RDATE, count(SEQNO) as antall, max(SEQNO) as makssekvens
from DATE_TO_SEQNO
group by dato
order by 1, 2;

Verify the mview's existence:

SELECT mview_name,rewrite_enabled,refresh_mode,refresh_method, last_refresh_type, last_refresh_date,last_refresh_end_time,staleness,compile_state
FROM USER_MVIEWS;

MVIEW_NAME	REWRITE_ENABLED	REFRESH_MODE	REFRESH_METHOD	LAST_REFRESH_TYPE	LAST_REFRESH_DATE	LAST_REFRESH_END_TIME	STALENESS	COMPILE_STATE
SEQ_AGGR_INFO	Y	COMMIT	FAST	COMPLETE	18.01.2019 13:58:24	18.01.2019 13:58:24	FRESH	VALID

Verify the mview log's existence:

SELECT master,log_table,rowids, primary_key,filter_columns, include_new_values
FROM USER_MVIEW_LOGS;

MASTER	LOG_TABLE	ROWIDS	PRIMARY_KEY	FILTER_COLUMNS	INCLUDE_NEW_VALUES
DATE_TO_SEQNO	MLOG$_DATE_TO_SEQNO	YES	NO	YES	YES

The following query will now use the materialized view, due to the QUERY REWRITE directive used in the creation of the mview:

var B1 VARCHAR2(10);
EXEC :B1 := to_date('01.01.2018','dd.mm.yyyy');
set lines 200
set autot on
set timing on
select max(seqno)
from DATE_TO_SEQNO
where rdate = :B1;

The explain plan verifies it:

MAX(SEKVENSNUMMER)
------------------
          18580449

Elapsed: 00:00:00.05

Execution Plan
----------------------------------------------------------
Plan hash value: 1856567295

--------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name                   | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                        |     1 |    14 |   243   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE               |                        |     1 |    14 |            |          |
|*  2 |   MAT_VIEW REWRITE ACCESS FULL| SEQ_AGGR_INFO          |     1 |    14 |   243   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter("SEQ_AGGR_INFO"."RDATE"=:B1)

To drop the materialized view and its log object:

drop materialized view log on DATE_TO_SEQNO;
drop materialized view SEQ_AGGR_INFO;

Sources:
Create Materialized View Log

Create Materialized view

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