物化视图使用HAVING子句快速刷新？

Question

在Oracle 11g上,我试图创建一个FAST REFRESH ON COMMIT包含HAVING子句的物化视图.

该数据库数据仓库指南说:

快速刷新的一般限制

物化视图的定义查询限制如下:

• 它不能包含带子查询的HAVING子句.

但是如果我HAVING count(*)>1向其他工作的物化视图添加(注意:没有子查询),我会收到此错误:

ORA-12054:无法为实例化视图设置ON COMMIT刷新属性

dbms_mview.explain_mview() 说:

REFRESH_FAST                   N
REFRESH_FAST_AFTER_INSERT      N   2011 a HAVING clause is present

实际命令:

SQL>  create materialized view mv1 refresh fast on commit as
  2      select UserId, count(*) from USERS group by UserId;

Materialized view created.

SQL> DROP MATERIALIZED VIEW mv1;

Materialized view dropped.

SQL> create materialized view mv1 refresh fast on commit as
  2      select UserId, count(*) from USERS group by UserId
  3          having count(*)>1; -- the only difference
    having count(*)>1
                    *
ERROR at line 5:
ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

注意:已创建物化视图日志(否则即使第一个示例也不起作用).

为什么不起作用？有没有人知道带有HAVING子句的MV示例？所以至少我可以从那里开始(我用谷歌搜索但没有找到).

注意2:我想要的原因HAVING是将视图中的行数从数千甚至数百万减少到几个.节省存储(并可能获得性能).

PS:使用的精确Oracle数据库版本:11.2.0.3.0

Answer 1

是的，文档似乎不准确。

作为解决方法，您可以尝试实现嵌套物化视图。

CREATE MATERIALIZED VIEW mv1 
REFRESH FAST ON COMMIT 
AS
SELECT col1,
       COUNT(col1) count_col1
FROM test_table
GROUP BY col1

ALTER MATERIALIZED VIEW mv1 ADD CONSTRAINT pk_mv1 PRIMARY KEY (col1)

CREATE MATERIALIZED VIEW LOG ON mv1 WITH PRIMARY KEY;

CREATE MATERIALIZED VIEW MV2 
REFRESH FAST ON COMMIT AS
SELECT col1,
       count_col1
FROM   mv1
WHERE  count_col1 > 1