学步园

(1)MySQL解决方案：
select datediff(xj_date,xz_date)
from(
     select rdr_date as xj_date
     from readrinfo
     where rdr_name = 'xiaojie'
    ) x,
   (
    select rdr_date as xz_date
    from readrinfo
    where rdr_name = 'xiaozhao'
   ) y
;
(2)SQL Server解决方案：就是交换datediff函数中的参数的位置且增加‘day’，

例：datediff(day,xz_date,xj_date).