相关疑难解决方法(0)

我正在使用SQL Server 2005.我想将列中的值限制为唯一,同时允许NULLS.

我当前的解决方案涉及视图上的唯一索引,如下所示:

CREATE VIEW vw_unq WITH SCHEMABINDING AS
    SELECT Column1
      FROM MyTable
     WHERE Column1 IS NOT NULL

CREATE UNIQUE CLUSTERED INDEX unq_idx ON vw_unq (Column1)

有更好的想法吗？

考虑到以下关系:

class Style < ActiveRecord::Base
  has_many :stylefeatures, :dependent => :destroy
  has_many :features, :through => :stylefeatures
end

class Stylefeature < ActiveRecord::Base
  belongs_to :style
  belongs_to :feature
end

class Feature < ActiveRecord::Base
  has_many :stylefeatures, :dependent => :destroy
  has_many :styles, :through => :stylefeatures
end

如何在Style模型中最有效地添加索引以加速此方法:

  def has_feature? (arg)
    self.features.where(:name=>arg).exists?
  end