1问题描述：根据始末日期查询数据，由于数据库数据量大，用between and很慢，就添加了year,month,day字段，在比较年月日的时候有substr和date两种方法，两种都尝试过每次加载时间都在变化，也没找到相关的技术文章。理论上是两种速度都差不多，还是有相对快的方法？感谢每一个答题者。
2.相关代码片段：

//substr
if(substr($startTime,0,4) == substr($endTime,0,4)){
    $str .= " L.year = ".substr($startTime,0,4);
    if(substr($startTime,4,2) == substr($endTime,4,2)){
        $str .= " and L.month = ".substr($startTime,4,2);
        if(date('Ynd',strtotime($startTime)) == date('Ynd',strtotime($endTime))){
            $str .= " and day = ".date('d',strtotime($startTime));
        }else{
            $str .= " and log_date between '$startTime' and '$endTime' ";
        }
    }else{
        $str .= " and log_date between '$startTime' and '$endTime' ";
    }
}else{
    $str .= " L.log_date between $startTime and $endTime";
}

//date

 if(date('Y',strtotime($startTime)) == date('Y',strtotime($endTime))){
        $str = " where year = ".date('Y',strtotime($startTime));
        if(date('Yn',strtotime($startTime)) == date('Yn',strtotime($endTime))){
            $str .= " and month = ".date('n',strtotime($startTime));
            if(date('Ynd',strtotime($startTime)) == date('Ynd',strtotime($endTime))){
                $str .= " and day = ".date('d',strtotime($startTime));
            }else{
                $str .= " and log_date between '$startTime' and '$endTime' ";
            }
        }else{
            $str .= " and log_date between '$startTime' and '$endTime' ";
        }
    }else{
        $str = " where log_date between '$startTime' and '$endTime' ";
    }