select count(1) 
from ba_purchase
where date>=? and data<=?
group by sp_code
having count(purchase_code)>1

------解决方案--------------------

select count(distinct purchase_code)
 from ba_purchase
  where sp_code = 企业编号
  and date between 开始日期 and 截止日期;
   
select count(*)
 from (select *
         From ba_purchase
        where date between 开始日期 and 截止日期
        group by sp_code, purchase_code
       having count(*) > 1);