仅是产品的限制. SQL Server 2005+确实允许这样做.

Just a limitation of the product. SQL Server 2005+ does allow this.

由于提示点单列除非值严重偏斜(在2008年过滤索引可以提供帮助的情况下)，否则索引不太可能很有用.

Because of the Tipping Point a single column bit index is unlikely to be very useful unless the values are heavily skewed (a scenario for which filtered indexes in 2008 can help)

仍然-仍然可以用作复合覆盖索引的一部分.

Still - could be useful as part of a composite covering index though.