关于mysql 自定义@row的使用

• 应用场景:在对成绩或者积分排名时,往往需要显示排名;

  • 成绩排名:相同分数的人,名次相同

    Select s.Score,
        case 
          when @rowtotal = s.Score then cast(@rownum as SIGNED  INTEGER) # 当这个成绩和@rowtotal上一次的成绩相同时,@rownum不变
          when @rowtotal := s.Score then cast(@rownum :=@rownum +1 as SIGNED  INTEGER) # 当取到的成绩和上一次成绩不同时, @rownum +1 ,rank排名加一
          when @rowtotal = 0 then cast(@rownum :=@rownum +1 as SIGNED  INTEGER) # 当取到的成绩为0时,排名+1
        end as Rank 
    from 
    (select Id,Score from Scores order by Score desc)s, # 通过分数倒序排列成绩
    (Select @rownum :=0,@rowtotal :=null) r	#这个是关键,@rownum,@rowtotal先置空,然后和上边的成绩关联
    

  • 积分排名:按积分插入时间排名

    SELECT
        obj.score,@rownum := @rownum + 1 AS Rank
    FROM
        (
            SELECT
                user_id,
                score
            FROM
                `sql_rank`
            ORDER BY
                score DESC,
                update_time ASC
        ) AS obj,
        (SELECT @rownum := 0) r
    

    我遇到的问题是,排名显示的是1.0,2.0的double类型,所以我用cast(@rownum as SIGNED INTEGER)转化了一下