What types of materialized views can be created in an Oracle database?

There are three types of Materialized Views that can be created in an Oracle database:

1. Materialized Views with Aggregates

* The most commonly used materialized view, particularly in Datawarehouse databases.

Example:

CREATE MATERIALIZED VIEW SEQ_AGGR_INFO 
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;

Requirements:

* The SELECT-list must contain all of the GROUP BY columns (if present)
* There must be a COUNT(*) and a COUNT(column) on any aggregated columns.
* A materialized view logs must be present on all tables referenced in the query that defines the materialized view.
* Valid aggregate functions are: SUM, COUNT(x), COUNT(*), AVG, VARIANCE, STDDEV, MIN, and MAX.

2. Materialized Views containing only joins

* Materialized views contain only joins and no aggregates

Example:

CREATE MATERIALIZED VIEW active_data
TABLESPACE data1
CACHE
REFRESH FORCE ON COMMIT
WITH PRIMARY KEY
ENABLE QUERY REWRITE
AS
SELECT 
    act.q_id, 
    act.doc_type, 
    act.next_q_id, 
    act.prev_q_id,
    act.created, 
    act.created_by, 
    act.last_modified, 
    act.last_modified_by, 
    act.contents, 
    act.accum_value, 
    act.accum_total
FROM active_data act JOIN archived_data arc
ON arc.q_id = act.q_id;

An advantage with these types of materialized views is that expensive joins are precalculated.
Only REFRESH ON COMMIT or REFRESH ON DEMAND is legal with mviews containing only joins. When ON COMMIT is used, the refresh is performed at commit time of the transaction that does DML on the materialized view's detail table.


3. Nested Materialized Views

* A nested materialized view is a materialized view whose definition is based on another materialized view.

I have no personal experience using this type of materialized view, but Oracle has supplied some examples if you follow the link above.

Sources: Oracle 12.2 Data Warehousing Guide

What is a "fast refresh" of materialized views?

A FAST REFRESH of a materialized view applies only changed data to the materialized view. This way you don't have to rebuild the materialized view every time data in the base tables' change. Oracle keeps a log of changed data in a different object called a materialized view log.

To indicate a FAST REFRESH, use the following syntax:

CREATE MATERIALIZED VIEW SEQ_AGGR_INFO
REFRESH FAST ON COMMIT | ON DEMAND | ON STATEMENT | START WITH SYSDATE NEXT SYSDATE+1/24/60
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;

ON COMMIT instructs oracle to refresh the materialized view whenever a transaction against the master table commits.

ON DEMAND instructs oracle that the materialized view should not be refreshed unless the user manually executes one of the DBMS_MVIEW refresh procedures.

ON STATEMENT instructs oracle to automatically refresh refresh the materialized view every time a DML operation is performed on any of the materialized view's base tables.

START WITH specifies a datetime expression for the first automatic refresh time. NEXT indicates the interval between automatic refreshes

General restrictions for FAST REFRESH are listed here

How to troubleshoot query rewrites

1. Run the script $ORACLE_HOME/rdbms/admin/utlxrw.sql logged in as the schema who owns the materialized view.

2. Analyze the query by logging on as the schema owning the materialized view and execute:

set serveroutput on

begin
      DBMS_MVIEW.EXPLAIN_REWRITE('select dato, max(sekvensnummer)'||
            'from DATE_TO_SEQNUM where dato <= :B1 group by dato','SEQ_AGGREGATED','x');
end;
/

where the first argument is the one you expect to use query rewrite, and the second argument is the name of the materialized view. 3. The potential reasons for the failed rewriting can be found in the table REWRITE_TABLE:

select message from rewrite_table;

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

Datawarehousing guide

How to solve ORA-01031: insufficient privileges when creating a materialized view

At first, I got the following error from the Oracle server when exeuting the "CREATE MATERIALIZED VIEW" script:

where    tab2.year >   to_number(to_char(sysdate, 'YYYY')) - 4
                                       *
ERROR at line 36:
ORA-01031: insufficient privileges

Solution:
If you try to create a materialized view based on tables in a different schema, you need the privilege

GLOBAL QUERY REWRITE

as well as

CREATE TABLE
CREATE MATERIALIZED VIEW

Grant the privileges:

grant GLOBAL QUERY REWRITE to scott;
grant CREATE TABLE to scott;
grant CREATE MATERIALIZED VIEW to scott;

Verify your users privileges:

connect scott/tiger

select * from user_sys_privs;


USERNAME                       PRIVILEGE                                ADM
------------------------------ ---------------------------------------- ---
EKSTERN                        CREATE SESSION                           NO
EKSTERN                        CREATE TABLE                             NO
EKSTERN                        CREATE MATERIALIZED VIEW                 NO
EKSTERN                        GLOBAL QUERY REWRITE                     NO

This should fix your ORA-01031 problems.

Source: Oracle Support "Create Local Materialized View with Query Rewrite Option Fails with ORA-1031 Insufficient Privileges" (Doc ID 1079983.6)