The second rule is that indexes must be written with sparse columns in mind.
第二个规则是，要时刻记住尽量使用Sparse列进行索引。
SQL Server 2008 has lifted the limit of 1024 columns per table with a new option called "sparse columns".
SQLServer 2008消除了每个表只能有1024个列的限制，这是通过一个名叫“稀疏列（sparse columns）”的选项来实现的。
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。
You might receive errors if you try to generate data for a table that contains SPARSE columns and a COLUMN_SET.
如果您尝试对包含SPARSE资料行和COLUMN_SET的资料表产生资料，则可能会收到错误。
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.
ColumnSet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ColumnSet列。
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.
ColumnSet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ColumnSet列。
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