codeigniter活动记录中的子查询和子句

Question

如何将此查询转换为codeigniter活动记录？我已经尝试过使用活动记录的子句但是当我使用它时它没有用。

SELECT *

FROM   schedule

WHERE  `date` >= '2016-08-15' AND 

   `date` <= '2016-08-21' AND

    emp_id IN (SELECT   emp_id

               FROM     schedule

               WHERE    `date` >= '2016-08-15' AND `date` <= '2016-08-21'

               GROUP BY emp_id

               HAVING   COUNT(DISTINCT `date) = 7)