如何在視圖中更改虛擬列的數據類型？

Question

create or replace view ABC_VIEW(
   VEHICLEID, BRAND,
   MODEL, VEHICLE_TYPE,
   FUEL_TYPE, TRANSMISSION_TYPE,
   GEARBOX, DRIVE_TYPE,
   VEHICLE_NUMBER, PRICE, 
   "TEST Column"
) as 
  select VEHICLEID, BRAND,
         MODEL, VEHICLE_TYPE,
         FUEL_TYPE, TRANSMISSION_TYPE,
         GEARBOX, DRIVE_TYPE,
         VEHICLE_NUMBER, PRICE, 
         '' as "TEST Column" 
    from ABC;

默認情況下， "Test Column"創建為Char(1) 。 如何將其更改為Number數據類型？

請幫幫我。 謝謝。

Answer 1

像這兒：

create or replace view v_abc as 
  select cast(null as number) test_column
    from dual;

測試：

select table_name, column_name, data_type 
  from all_tab_columns where table_name='V_ABC';

TABLE_NAME                     COLUMN_NAME                    DATA_TYPE 
------------------------------ ------------------------------ -------
V_ABC                          TEST_COLUMN                    NUMBER

Answer 2

您可能正在尋找TO_NUMBER函數。

嘗試這個：

create or replace view ABC_VIEW
(VEHICLEID,BRAND,MODEL,VEHICLE_TYPE,FUEL_TYPE,TRANSMISSION_TYPE,GEARBOX,DRIVE_TYPE,VEHICLE_NUMBER,PRICE,**"TEST Column"**) 
as select  VEHICLEID,BRAND,MODEL,VEHICLE_TYPE,FUEL_TYPE,
TRANSMISSION_TYPE,GEARBOX, DRIVE_TYPE,VEHICLE_NUMBER,PRICE,TO_NUMBER('') 
 from ABC;