Once the table has columnset defined, the select * will hide all sparse columns, and only see the column set.

一旦表中定义了columnset列，select *语句将会隐藏所有的Sparse列，代之以这个columnset列。

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Column sets have to part of a table's original design. If a table has any sparse columns in it, a column set cannot be added.

Column Set列必须在表的原始设计中进行定义，如果表中已经有了任意一个Sparse列，就不允许再添加Column Set列。

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Through analyzing the characteristics of sparse data, we conclude that it's suitable for column-oriented database to store sparse data and give the method of how to design sparse database.

结合列存储数据库系统与稀疏数据自身的特点，本文提出了一种列存储数据库系统适宜存储稀疏数据的观点，并给出稀疏数据库的设计方式。

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