Using views also helps insulate the application when the underlying table definition changes.
底层表定义发生变化时，使用视图还有助于使应用程序不受到影响。
The table, which is named SALES_SUMMARY, is based on the underlying table SALES in the SAMPLE database.
该表名为 SALES_SUMMARY，它基于 SAMPLE 数据库中的底层表 SALES。
The summary table, which is named EMP_SUMMARY, is based on the underlying table EMPLOYEE in the SAMPLE database.
总结表名为EMP _ SUMMARY，它基于SAMPLE数据库中的底层表employee。
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