我在为聚合创建物化视图时遇到了一个问题。如果源表上出现DML,则物化视图应该自动刷新并显示更新后的结果。这个想法是存储聚合结果并直接获取数字,而不是进行查询,我基本上想看看这是否符合我们的目标。我们的表每天将有多达300万次插入。
例8-3例3:创建物化视图我做了:CREATE MATERIALIZED VIEW LOG ON table WITH SEQUENCE, ROWID
(SUBJECTID)
INCLUDING NEW VALUES;
CREATE MATERIALIZED VIEW ih_data_aggregated_view
PARALLEL
BUILD IMMEDIATE
REFRESH FAST ON COMMIT
AS
SELECT SUBJECTID ,count(*)as totalcount ,avg(price)as avgprice,sum(price) as totalprice
FROM table
WHERE SUBJECTID='xxxxx' GROUP by SUBJECTID;
但是这得到:
java.sql。SQLException: sqllexception: ORA-12054:无法为物化视图设置ON COMMIT刷新属性
文档包含了对物化视图和带有聚合的物化视图的一般限制。
虽然处理这些列表是有指导意义的,但您可以通过检查dbms_mview.explain_mview
过程的结果来查看是否可以快速刷新现有或潜在的物化视图:
set serveroutput on
declare
msg_array SYS.ExplainMVArrayType;
begin
dbms_mview.explain_mview (q'[
SELECT SUBJECTID ,count(*)as totalcount ,avg(price)as avgprice,sum(price) as totalprice
FROM your_table
WHERE SUBJECTID='xxxxx'
GROUP by SUBJECTID
]',
msg_array);
for i in msg_array.first..msg_array.last loop
dbms_output.put_line(rpad(msg_array(i).capability_name, 30)
||' '|| msg_array(i).possible
||' '|| msg_array(i).msgtxt);
end loop;
end;
/
...
REFRESH_FAST F
...
REFRESH_FAST_AFTER_INSERT F agg(expr) requires correspondng COUNT(expr) function
REFRESH_FAST_AFTER_ONETAB_DML F SUM(expr) without COUNT(expr)
REFRESH_FAST_AFTER_ONETAB_DML F see the reason why REFRESH_FAST_AFTER_INSERT is disabled
REFRESH_FAST_AFTER_ANY_DML F see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled
REFRESH_FAST_PCT F PCT is not possible on any of the detail tables in the materialized view
...
正如@vercelli所提到的,以及REFRESH_FAST_AFTER_INSERT
消息所建议的,您需要将count(*)
更改为count(price)
。但这并不是故事的全部;如果你只是改变它,你会看到:
REFRESH_FAST F
...
REFRESH_FAST_AFTER_INSERT F mv log does not have all necessary columns
REFRESH_FAST_AFTER_ONETAB_DML F see the reason why REFRESH_FAST_AFTER_INSERT is disabled
REFRESH_FAST_AFTER_ONETAB_DML F COUNT(*) is not present in the select list
REFRESH_FAST_AFTER_ANY_DML F see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled
您的物化视图日志必须包含您正在聚合的列:
CREATE MATERIALIZED VIEW LOG ON your_table WITH SEQUENCE, ROWID
(SUBJECTID,PRICE)
INCLUDING NEW VALUES;
Materialized view LOG created.
CREATE MATERIALIZED VIEW ih_data_aggregated_view
PARALLEL
BUILD IMMEDIATE
REFRESH FAST ON COMMIT
AS
SELECT SUBJECTID ,count(price)as totalcount ,avg(price)as avgprice,sum(price) as totalprice
FROM your_table
WHERE SUBJECTID='xxxxx'
GROUP by SUBJECTID;
Materialized view IH_DATA_AGGREGATED_VIEW created.
缺失的count(*)
仍然会被报告,但由于这是针对单个表的,因此不会阻止快速刷新。值得注意的是,如果你的price
列是空的,那么count(price)
和count(*)
可能会给出不同的结果;如果是这种情况,您可能希望将这两个计数作为MV中的列。