解决case when索引失效的问题

查询语句中包含case when 计算公式，类似

select name, sum(case when a*b*100>30 then 1 else 0 end) as cnt from tab
grouby by name

改为计算公式在后面，类似

select name, sum(case when 30<a*b*100 then 1 else 0 end) as cnt from tab
grouby by name