mysql怎么给查询的结果表增加一列自增列

举例：
SELECT
@rownum := @rownum+1 AS id,t.XH, t.CFXFBHLB
FROM
(SELECT @rownum:=0)r , t_xfcf_tq as t

说明：
SELECT
@rownum := @rownum+1 AS id , (t.字段)
FROM
(SELECT @rownum:=0)r , (表名) as t