mysql order by 索引问题

Question

SELECT
    umb.m AS id,
    umb.s AS STATUS,
    pm.c AS ct,
    pm.v AS vt,
    pm.u AS ut,
    pm.a AS attribute 
FROM
    u umb,
    p pm 
WHERE
    pm.id = umb.m
    AND umb.u = '****' 
    AND ( pm.p = 0 OR pm.p = 1 ) 
ORDER BY
    pm.c DESC
    

这里用了两个表：u和p
explain的结果是：
p表是全表查询，extra是 Using where; Using filesort
请教下如何优化查询速度呢，如果是加索引，如何加呢，谢谢### 问题描述