DB2 MATERIALIZED QUERY TABLE

Materialized Query Table(MQT)

1. A materialized query table is a table whose structure and definition are based on the result of a given query.
2. Materialized query table gets its data from the same query. And MQT actually contains that data.
3. That query may contain more than 1 table.

Syntax for MQT

CREATE TABLE mqt-name AS (select-statement) mqt-options

for example

CREATE TABLE TRANS_REPORT AS 
(SELECT YEAR AS SYEAR, MONTH AS SMONTH, DAY AS SDAY, SUM(AMOUNT) AS SSUM FROM TRANS                             
GROUP BY YEAR, MONTH, DAY )
DATA INITIALLY DEFERRED         
REFRESH DEFERRED                    
MAINTAINED BY USER

MQT Options details

REFRESH TABLE

How MQT will get data when created with “DATA INITIALLY DEFERRED,” or How MQT will get updated when created with the “REFRESH DEFERRED” option. The answer is the “REFRESH TABLE” statement.

REFRESH TABLE TRANS_REPORT

This will update all the data of MQT using the given “select-statement

.”

Convert a simple table into MQT.

Let say you created a table:

CREATE TABLE TRANSCOUNT (ACCTID SMALLINT NOT NULL,  LOCID SMALLINT, YEAR DATE , CNT INTEGER)

And for some reason, you want to convert this same table into MQT. Use ALTER TABLE Statement.

ALTER TABLE TRANSCOUNT
		ADD MATERIALIZED QUERY
		(SELECT ACCTID, LOCID, YEAR, COUNT(*) AS CNT FROM                TRANS GROUP BY ACCTID, LOCID, YEAR )
		DATA INITIALLY DEFERRED
		REFRESH DEFERRED
                MAINTAINED BY USER

And your table is now MQT.

If you want to convert your MQT back to your simple table, again use ALTER TABLE

ALTER TABLE TRANSCOUNT  DROP MATERIALIZED QUERY

NOTE: In this post, most of the queries are copied from somewhere else. I forgot the source. So as soon as I remember the source detail, I will update this post with the details.