每天生成 N 个中奖机会到奖池，从奖池进行抽奖，代码数据库操作部分依赖 Codeigniter。

lucky_draw_from_pool.php

<?php

    //CREATE TABLE IF NOT EXISTS `pool` (
    //`id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
    //`active_time` datetime NOT NULL COMMENT '活动时间',
    //`used_time` datetime DEFAULT NULL COMMENT '被使用时间',
    //`status` tinyint(4) NOT NULL,
    //PRIMARY KEY (`id`),
    //KEY `active_time_status` (`active_time`,`status`)
    //) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

    /**
     * 构造奖池（按每天所需中奖数量）
     * 该方法为手动操作方法，连同 GET 形势的密钥访问，用以重建或清空奖池
     * @author luyuz
     */
    public function set_up_pool()
    {
        if ($this->admin_key != $this->input->get('admin_key', TRUE)) {
            die('Admin Key ERROR!');
        }

        /**
         * 是否要清空未抽奖池
         */
        $is_empty = $this->input->get('is_empty', TRUE) ? $this->input->get('admin_key', TRUE) : TRUE;

        /**
         * 每天生成多少个中奖机会
         */
        $everyday_quantity = $this->input->get('everyday_quantity', TRUE) ? $this->input->get('everyday_quantity', TRUE) : 30;

        /**
         * 开始生成日期（含）
         */
        $start_date = $this->input->get('start_date', TRUE) ? $this->input->get('start_date', TRUE) : '20130522';

        /**
         * 结束生成日期（含）
         */
        $end_date = $this->input->get('end_date', TRUE) ? $this->input->get('end_date', TRUE) : '20130613';

        // 开始从时间范围内生成时间戳
        $start_timestamp = mktime(00, 00, 00, substr($start_date, 4, 2), substr($start_date, 6, 2), substr($start_date, 0, 4));
        $end_timestamp = mktime(23, 59, 59, substr($end_date, 4, 2), substr($end_date, 6, 2), substr($end_date, 0, 4));


        $timestamp_list = array();
        $curr_day = $start_timestamp;
        $curr_day_add = strtotime('+1 day', $start_timestamp);


        while ($curr_day <= $end_timestamp) {
            for ($o = 0; $o < $everyday_quantity; $o++) {
                $timestamp = rand($curr_day, $curr_day_add);
                $timestamp_list[] = date("Y-m-d H:i:s", $timestamp);
            }
            $curr_day = strtotime('+1 day', $curr_day);
            $curr_day_add = strtotime('+1 day', $curr_day);
        }

        // 清空未抽奖池
        if ($is_empty) {
            $this->db->delete($this->table['pool'], array('status' => 0));
        }

        // 写入数据库
        sort($timestamp_list);
        foreach ($timestamp_list as $row) {
            $data = array(
                'active_time' => $row,
                'status' => 0,
            );
            $this->db->insert($this->table['pool'], $data);
        }

        die('Finish!');
    }

    /**
     * 以当前时间从奖池抽奖一次
     */
    private function _lucky_draw()
    {
        $now = date("Y-m-d H:i:s");

        $this->db->where(array('status' => 0, 'active_time <=' => $now));
        $this->db->limit(1);
        $this->db->update($this->table['pool'], array('status' => 1, 'used_time' => $now));

        if ($this->db->affected_rows() > 0) {
            return TRUE;
        } else {
            return FALSE;
        }
    }

?>