以不规则的时间间隔自动刷新物化视图

Question

我需要以不规则的间隔自动刷新物化视图，例如0800hrs，1200hrs 1800hrs和2200hrs。我只能定期安排刷新，如下所示

...

REFRESH FORCE ON DEMAND START WITH sysdate+0 NEXT sysdate+(6/24)
AS Select * from Employee;

Answer 1

您可以在CASE中添加NEXT声明。所以你可以做类似

的事情

NEXT (CASE WHEN to_number( to_char( sysdate, 'HH24' )) >= 22 
           THEN trunc(sysdate+1) + interval '8' hour
           ...
           ELSE null
       END)

为了一般的理智，我通常会创建一个新函数（即get_next_refresh_time）来实现这个CASE语句，并在物化视图中引用该函数。

CREATE OR REPLACE FUNCTION get_next_refresh_time 
  RETURN DATE
IS
  l_dt DATE;
BEGIN
  SELECT CASE WHEN to_number( to_char( sysdate, 'HH24' )) >= 22 
              THEN trunc(sysdate+1) + interval '8' hour
              WHEN to_number( to_char( sysdate, 'HH24' )) <  8
              THEN trunc(sysdate) + interval '8' hour
              WHEN to_number( to_char( sysdate, 'HH24' )) between 8 and 11
              THEN trunc(sysdate) + interval '12' hour
              WHEN to_number( to_char( sysdate, 'HH24' )) between 12 and 17
              THEN trunc(sysdate) + interval '18' hour
              WHEN to_number( to_char( sysdate, 'HH24' )) between 18 and 21
              THEN trunc(sysdate) + interval '22' hour
              ELSE null
          END
    INTO l_dt
    FROM dual;
  RETURN l_dt;
END;

NEXT get_next_refresh_time;

Answer 2

我喜欢使用DBMS_SCHEDULER并设置一个作业来调用DBMS_MVIEW.REFRESH（参见http://docs.oracle.com/cd/B28359_01/appdev.111/b28419/d_mview.htm#ARPLS027）。这也为您的刷新提供了更多选项。