看来您的数据模型未规范化。您应该考虑有关创建其他表的建议。

下面是一个非常丑陋的查询，它检查日期是否在三个范围内，然后返回匹配率。

select case 
        when date '2010-12-05' between range1_from and range1_to then range1_rate
        when date '2010-12-05' between range2_from and range2_to then range2_rate
        when date '2010-12-05' between range3_from and range3_to then range3_rate
       end as rate
  from events
 where date '2010-12-05' between range1_from and range1_to
    or date '2010-12-05' between range2_from and range2_to
    or date '2010-12-05' between range3_from and range3_to;