SQLServer CASE WHEN 用法

SELECT sc.NAME AS 学校名称
    ,xueyuan.NAME AS 院系
    ,StudentNo AS 学号
    ,st.StudentName AS 学生姓名
    ,st.sex AS 性别
    ,st.IDCard AS 身份证
    ,st.Mail AS 邮箱
    ,st.Telephone AS 电话
    ,st.QQ   AS QQ
    ,CodeName AS 专业
    ,class.NAME AS 班级
    ,banzhuren.TeacherName as 班主任
    ,biyesheji.TeacherName as 毕业设计老师
    ,jiuye.TeacherName as 就业指导老师
    ,EnterpriseName AS 企业
    ,sct.TeacherName AS 学校指导老师
    ,etc.TeacherName AS 企业指导老师
    ,CONVERT(varchar(10),ApplyBeginTime,23) as 实习开始时间
    ,CONVERT(varchar(10),ApplyEndTime,23) as 实习结束时间    
    ,CASE
        WHEN BiYeIf <>1 THEN'未毕业' 
        else '已毕业'   
    END as '是否毕业'
    ,CASE
        WHEN BiYeIf <>1 THEN'未毕业'
        else CONVERT(varchar(10),BiYeTime,23)
    END as '毕业时间'
FROM dbo.WDCBS_Student AS st