MySLQ排序后标记排行

set @rownum=0;

SELECT @rownum:=@rownum+1 AS top, customer.*
FROM  customer

SELECT @rownum:=@rownum+1 AS top, customer.* 
FROM (SELECT @rownum:=0) r, customer ORDER BY customer.this_month_cost DESC

SELECT @rownum:=@rownum+1 AS top, customer.id
FROM (SELECT @rownum:=0) r, customer ORDER BY customer.this_month_cost DESC

UPDATE `customer` c,
 (
    SELECT
        @rownum :=@rownum + 1 AS rownum,
        customer.id
    FROM
        (SELECT @rownum := 0) r,
        customer
    ORDER BY
        customer.this_month_cost DESC
) a
SET c.top = a.rownum
WHERE
    c.id = a.id