null(特殊)，不能如下判断：select case e_base.e_base_fzjg when null then 1 else 3 end from e_base
只能：select case when e_base.e_base_fzjg is null then 1 else 3 end from e_base
也不能用：select case when e_base.e_base_fzjg = null then 1 else 3 end from e_base
select case when null is null then '是null' else '不是null' end select case when 'null' is null then '是null' else '不是null' end select case when null is null then '是null' else '不是null' end
.: 
