mysql带行号的查询

SELECT @rownum:=@rownum+1 AS rownum, cdate, SUM(cash_valid) AS sum_cv, SUM(cash_total) AS sum_ct 
FROM (SELECT @rownum:=0) r, `{$tab}` WHERE {$cri} GROUP BY cdate ORDER BY sum_cv desc

这样可以很方便的对某一字段进行排序。