物化表的使用疑问

select workdept,avg(empno) from employee group by workdept  




1、当我们查询相关表时，DB2会自动决定是使用原表还是使用物化查询表，不需要更改应用程序？

 
 
 
示例： 
 
code]CREATE TABLE emp_summary AS 
( 
SELECT 
workdept 
,COUNT(*) AS crows 
,SUM(empno) AS sumno 
FROM 
employee 
GROUP BY workdept 
) 
DATA INITIALLY DEFERRED 
REFRESH IMMEDIATE; 

定义了物化查询表后，如果我们执行以下SQL，DB2优化器将使用MQT
select workdept,avg(empno) from employee group by workdept  select workdept,avg(empno) from employee group by workdept
DB2 优化器将上面的SQL转化成下面这样
select workdept,sumno/crows from emp_summary
2、环境变量、dbm、db 参数需要做特别的设置吗？