創建填充，然後從視圖中刪除表（Oracle）

Question

我有一個視圖比較兩個表（tableYesterday和tableToday）中的數據並輸出基於比較的結果。讓我們調用這個視圖：ViewComp。

我需要做的比這更多。通過單一視圖，我實際上需要：

1. 創建或替換tableToday並預先填充它。
2. 執行ViewComp查詢。
3. 替換tableYesterday與tableToday。

我研究過像嵌套視圖這樣的東西，但是我找不到從視圖中執行1和3的方法。我會很感激任何想法。謝謝。

Answer 1

你不能做這種事。您可以創建PL/SQL過程來執行步驟或創建實體化視圖。

Answer 2

這幾乎肯定是一個壞主意。意見不應該「做」任何事情。

對於那些極少數情況下，這是必需的，它可以用下面的技巧來完成。你一定要記錄這段代碼，向其他人解釋你在做什麼以及爲什麼。

採樣模式和對象

--Create table. 
create table tableYesterday(a number, b number); 

--Create abstract data type to hold one row of data to be returned by the view. 
create or replace type ViewComp_type is object 
(
    a number, 
    b number 
); 

--Create nested table to hold multiple rows of data to be returned by the view. 
create or replace type ViewComp_nt is table of ViewComp_type; 

函數返回結果

--Create function to return data. 
create or replace function ViewComp_function return ViewComp_nt authid current_user as 
    --This pragma is necessary for a function that will perform DML. 
    pragma autonomous_transaction; 

    v_results ViewComp_nt; 

    v_name_already_exists exception; 
    pragma exception_init(v_name_already_exists, -955); 
begin 
    --Try to create today's table. Ignore errors if it exists. 
    begin 
     execute immediate 'create table tableToday(a number, b number)'; 
    exception when v_name_already_exists then 
     execute immediate 'truncate table tableToday'; 
    end; 

    --Populate today's table. 
    execute immediate 'insert into tableToday values(1,1)'; 

    --Get the difference. 
    execute immediate q'[ 
     select cast(collect(ViewComp_type(a,b)) as ViewComp_nt) 
     from 
     (
      select * from tableToday 
      minus 
      select * from tableYesterday 
     ) 
    ]' into v_results; 

    --Remove yesterday's data. 
    execute immediate 'truncate table tableYesterday'; 

    --Replace it with today's data. 
    execute immediate 'insert into tableYesterday select * from tableToday'; 
    commit; 

    --Return the difference. 
    return v_results; 
end; 
/

創建視圖返回函數的數據

create or replace view ViewComp as 
select * from table(ViewComp_function); 

測試運行

--First execution: 
select * from ViewComp; 

A B 
- - 
1 1 

--Second execution: 
select * from ViewComp; 

A B 
- -