NULL值in：conditions =＆gt;

Question

 Contract.all(:conditions => ['voided == ?', 0]).size
 => 364
 Contract.all(:conditions => ['voided != ?', 0]).size
 => 8
 Contract.all.size
 => 441

3个数字没有加起来（364 + 8！= 441）。编写:conditions来计算voided列值为NULL或等于零的行的正确方法是什么？

Answer 1

Contract.all(:conditions => {:voided => nil})

或

Contract.all(:conditions => ['voided IS NULL'])

Answer 2

 Contract.all(:conditions => ["voided is ?", nil]).size

 Contract.all(:conditions => ["voided is not ?", nil]).size