mysql count 中使用case when 带条件及去重

SELECT 
CASE (SELECT NOW() > '2019-02-12 16:48:00')
WHEN 1 THEN '男'
WHEN 2 THEN '女' 
ELSE '未知' 
END
as ages

　　

COUNT(CASE WHEN A.expire_time<{0} AND A.expire_time<>0 THEN A.expire_time END) AS disabled_total 

　对部分列去重

DISTINCT ucd.course_id,ucd.user_id and CASE WHEN ucd.kind=0 THEN ucd.kind END