sql case select

SELECT ID,TITLE,
(SELECT TIMES FROM CLS_COURSE WHERE CLS_COURSE.ID=CLS_CLASS.COURSEID) AS TIMES,
(SELECT CASE WHEN EXISTS(SELECT *  FROM CLS_ATDC WHERE CLS_ATDC.CLSID=CLS_CLASS.ID ) THEN (SELECT TOP 1 COURSETIME FROM CLS_ATDC WHERE CLS_ATDC.CLSID=CLS_CLASS.ID ORDER BY COURSETIME DESC) ELSE 0 END) AS CURRENTCOURSETIME
FROM CLS_CLASS WHERE ​​​DEPTID=@DEPTID​​​ AND ID IN (SELECT CLSID FROM CLS_DETAIL WHERE CLSDATE>=@BEGIN AND CLSDATE<​​=@END​​)