CActiveRecord中使用group语句问题 [ 未指定版本 ]

数据列

id, time char(14), money float(12,2)

ActiveRecord属性

id, time, money

现在想查找

select left(time, 8), sum(money) from _table_ group by left(time, 8) order by time asc

怎么处理呢

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        $criteria_income = new CDbCriteria();
        $criteria_income->select = 'left(time, 8) AS time, sum(money) AS money';
        // $criteria_income->addBetweenCondition('time', $start_date, $end_date);
        $criteria_income->group = 'left(time, 8)';
        $criteria_income->order = 'time ASC';