查询所有订单的最新信息的SQL语句的写法 DISTINCT配合count和group by一起完成

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场景：每个订单会持续更新，客户需要能查看每次更新的内容，所以每次更新我都会存一次，而不是在原来的基础上更新。

现在需要查看每个订单的最新信息。

SELECT *,count(DISTINCT ordernum) FROM xxxx group by ordernum order by addtime desc

Array(    [0] => Array        (            [id] => 24            [userid] => 3            [ordernum] => 1305090124            [is_completed] => 1            [card] => BBJ            [totaltime] => 100            [usedtime] =>             [addtime] => 1368088986            [filter_flag] => 201305            [is_read] => 0            [count(DISTINCT ordernum)] => 1        )    [1] => Array        (            [id] => 20            [userid] => 3            [ordernum] => 13042501001            [is_completed] => 1            [card] => A318            [totaltime] => 100            [usedtime] => 100            [addtime] => 1367477250            [filter_flag] => 201305            [is_read] => 1            [count(DISTINCT ordernum)] => 1        )    [2] => Array        (            [id] => 10            [userid] => 3            [ordernum] => 13042501002            [is_completed] => 1            [card] => G450            [totaltime] => 100            [usedtime] => 10            [addtime] => 1367475890            [filter_flag] => 201305            [is_read] => 1            [count(DISTINCT ordernum)] => 1        )    [3] => Array        (            [id] => 8            [userid] => 3            [ordernum] => 13042501005            [is_completed] => 1            [card] => BBJ            [totaltime] => 50            [usedtime] => 20            [addtime] => 1367458523            [filter_flag] => 201305            [is_read] => 1            [count(DISTINCT ordernum)] => 1        ))