Store the data from Materialized Views - oracle11g

Question

I have a materialized view(MV) which will refresh everyday at 23:00. It will select from a large transaction table (e.g. 100 million of records) and summarize the data which to be used in reporting purposes.
The MV is very simple just contain 4 columns and 7 records. Each time when user generate the report, it will always show the data as in the MV. Now user request to be able to view back the data of last year. Due to my MV always replace existing data, I am not able to achieve the user request.
My question
1. Is it possible to store the data in MV automatically in a persistent table?
2. Is it feasible to create a trigger to insert the data in MV to another table each time the MV is refresh complete?

Answer 1

Materialised Views do not have triggers. However, Updatable Materialized View does have triggers but it has a catch to it, it must be based upon a single table.
Based on more than one table
CREATE MATERIALIZED VIEW LOG ON EMP;
CREATE MATERIALIZED VIEW mv_test
REFRESH FAST WITH PRIMARY KEY
FOR UPDATE
AS
SELECT *
FROM emp em JOIN DEPT de ON EM.DEPTNO = DE.DEPTNO;
ORA-12013: updatable materialized views must be simple enough to do fast refresh
Based on single table
CREATE MATERIALIZED VIEW mv_test
REFRESH FAST WITH PRIMARY KEY
FOR UPDATE
AS
SELECT * FROM emp;
Materialized View created.
Trigger
CREATE OR REPLACE TRIGGER test_tg
BEFORE INSERT OR UPDATE OF ENAME, MGR
ON MV_TEST
REFERENCING NEW AS New OLD AS Old
FOR EACH ROW
DECLARE
tmpVar NUMBER;
BEGIN
tmpVar := 0;
NULL;
-- do as per the logic
EXCEPTION
WHEN OTHERS
THEN
NULL;
-- Consider logging the error and then re-raise
RAISE;
END test_tg;
Trigger created.
If the requirement is to have historical data, why not consider a standard transactional table to have data persistence using a Stored Procedure which is possible to execute using scheduler jobs.
As you have cited querying a large table which has 100 million records, my reckoning would be to use FOLL ALL or BULK COLLECT or consider batch processing, needless to say; this is a different topic.
The below are pseudo codes for procedure and scheduler jobs, make changes as deemed necessary. Either use INSERT or MERGE
Procedure using INSERT
CREATE OR REPLACE PROCEDURE historical_records (p_emp_no emp.empno%TYPE)
IS
BEGIN
FOR rec IN ( SELECT ename, mgr, SUM (sal) tot_sal
FROM scott.emp
WHERE empno = p_emp_no
GROUP BY ename, mgr)
LOOP
INSERT INTO hist_table (empno,
ename,
mgr,
sal_tot)
VALUES (rec.empno,
rec.ename,
rec.mgr,
rec.tot_sal);
END LOOP;
END;
Procedure using MERGE
CREATE OR REPLACE PROCEDURE historical_records (p_emp_no emp.empno%TYPE)
IS
BEGIN
MERGE INTO hist_table trg
USING ( SELECT ename, mgr, SUM (sal) tot_sal
FROM scott.emp
WHERE empno = p_emp_no
GROUP BY ename, mgr) src
ON (trg.empno = src.empno)
WHEN MATCHED
THEN
UPDATE SET trg.ename = src.ename, trg.mgr = src.mgr
WHEN NOT MATCHED
THEN
INSERT (trg.empno, trg.ename, trg.sal_tot)
VALUES (src.empno, src.ename, src.tot_sal);
END;
Scheduler Job
BEGIN
DBMS_SCHEDULER.CREATE_JOB (
job_name => 'HIST_PROC_JOB',
job_type => 'PLSQL_BLOCK',
JOB_ACTION => 'BEGIN historical_records; END;',
start_date => SYSDATE,
repeat_interval => 'FREQ=DAILY;BYHOUR=23;BYMINUTE=05',
end_date => NULL,
enabled => TRUE,
comments => 'Historical data insertion');
END;
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