sql - 如何在 SQL 中使用 Cast（count 和 case 语句）获取百分比

Question

选择演员（（计数（当birthdayattendance ='yes'然后Student_ID为空结束时的不同情况）/count（不同的Student_ID））作为十进制（2,2））

 from #tmpcombined.

Issue : last step which is percentage is returning as 0.00 instead 0.50. There are two students out of 4 whose who attended school on their birthday. 

标签： sql

Answer 1

一些数据库进行整数除法。为了防止这种情况，我只乘以 1.0：

select (count(distinct case when birthdayattendancek = 'yes' then Student_ID end) * 1.0 /
        count(distinct Student_ID)
       )

cast()除法后的ing只是将结果转换为小数。