Oracle 12c --Invisible Columns 可隱藏列
2024-08-29 13:55:00
供稿：網友
Invisible Columns 可隱藏列 ( Oracle 12c release 1版本引入新功能 ) An invisible column is a user-specified column whose values are only visible when the column is explicitly specified by name. You can add an invisible column to a table without affecting existing applications, and make the column visible if necessary. 一個隱藏列的列是在指定列的值僅列時可見顯式指定的名字。您可以添加一個看不見的列一個表在不影響現有應用程序,如果必要的,可以使列可見。 In general, invisible columns help migrate and evolve online applications. A use case might be an application that queries a three-column table with a SELECT * statement. Adding a fourth column to the table would break the application, which expects three columns of data. Adding a fourth invisible column makes the application function normally. A developer can then alter the application to handle a fourth column, and make the column visible when the application goes live. 一般來說,看不見列幫助遷移和發展在線應用程序。一個用例可能是一個應用程序,該應用程序可以查詢一個三列的表 SELECT *聲明。第四列添加到表會破壞應用程序,預計三列的數據。添加第四個無形的列使應用程序正常運轉。開發人員可以改變應用程序來處理第四列,并使列可見當應用程序上線。 The following example creates a table PRoducts with an invisible column count, and then makes the invisible column visible: 下面的示例創建一個表 products一個隱藏列 ,然后使無形的列count可見: CREATE TABLE products ( prod_id INT, count INT INVISIBLE ); ALTER TABLE products MODIFY ( count VISIBLE ); See Also: Oracle Database Administrator’s Guide to learn how to manage invisible columns Oracle Database SQL Language Reference for more information about invisible columns 參見: Oracle數據庫管理員指南學習如何管理無形的列 Oracle數據庫SQL語言參考關于看不見的更多信息列
