ORA-12054：無法爲物化視圖設置ON COMMIT刷新屬性

Question

我在爲我們的聚合創建物化視圖時遇到問題。如果源表上出現DML，則實例化視圖應自動刷新並顯示更新後的結果。這個想法是存儲聚合結果，並直接獲取數字而不是查詢，我基本上想看看這是否符合我們的目標。我們的桌子每天將有多達300萬個插頁。

按照鏈接Example 8-3 Example 3: Creating a Materialized View我所做的：

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; 

不過這樣會：

java.sql.SQLException: SQLException: ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

Answer 1

文檔包括general restrictions on materialised view和materialised view with aggregates。

，同時通過這些名單的工作是有益的，你可以看到現有的或潛在的物化視圖是否可被從the dbms_mview.explain_mview procedure檢查結果快速刷新：

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提及，並作爲REFRESH_FAST_AFTER_INSERT消息提示，您需要將count(*)更改爲count(price)。但那不是整個故事;如果你只是改變你會看到：

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 

你的物化視圖日誌必須包括列您彙總：

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. 

缺少count(*)仍報告，但由於這是針對單個表它不能防止快速刷新。值得注意的是，如果您的price列可以爲空，則count(price)和count(*)可能會給出不同的結果;如果是這種情況，您可能希望將這兩個數字作爲MV中的列。