thinkphp中的分表方法

public function getPartitionTableName($data=array()) {
        // 对数据表进行分区
        if(isset($data[$this->partition['field']])) {
            $field   =   $data[$this->partition['field']];
            switch($this->partition['type']) {
                case 'id':
                    // 按照id范围分表
                    $step    =   $this->partition['expr'];
                    $seq    =   floor($field / $step)+1;
                    break;
                case 'year':
                    // 按照年份分表
                    if(!is_numeric($field)) {
                        $field   =   strtotime($field);
                    }
                    $seq    =   date('Y',$field)-$this->partition['expr']+1;
                    break;
                case 'mod':
                    // 按照id的模数分表
                    $seq    =   ($field % $this->partition['num'])+1;
                    break;
                case 'md5':
                    // 按照md5的序列分表
                    $seq    =   (ord(substr(md5($field),0,1)) % $this->partition['num'])+1;
                    break;
                default :
                    if(function_exists($this->partition['type'])) {
                        // 支持指定函数哈希
                        $fun    =   $this->partition['type'];
                        $seq    =   (ord(substr($fun($field),0,1)) % $this->partition['num'])+1;
                    }else{
                        // 按照字段的首字母的值分表
                        $seq    =   (ord($field{0}) % $this->partition['num'])+1;
                    }
            }
            return $this->getTableName().'_'.$seq;
        }else{
            // 当设置的分表字段不在查询条件或者数据中
            // 进行联合查询，必须设定 partition['num']
            $tableName  =   array();
            for($i=0;$i<$this->partition['num'];$i++)
                $tableName[] = 'SELECT * FROM '.$this->getTableName().'_'.($i+1);
            $tableName = '( '.implode(" UNION ",$tableName).') AS '.$this->name;
            return $tableName;
        }
}