如何提高這個php的mysql代碼？

Question

使用這些代碼我回復Rank的學生，其regd等於$regd。實際上，這是一個工作代碼。不過，我被朋友告知，在mysql語句中Distinct和Group By不應該一起使用。但作爲新手，我無法弄清楚如何在不使用Distinct的情況下實現它，因爲它不會返回沒有Distinct的行。任何人都可以建議我如何改進這些代碼？

<?php 
mysql_select_db($database_dbconnect, $dbconnect); 
$query_myrank = "SELECT Distinct regd, Name_of_exam, 
         Name_of_Student, TOTALSCORE, Rank 
       FROM (SELECT *, IF(@marks = (@marks := TOTALSCORE), 
           @auto, @auto := @auto + 1) AS Rank 
         FROM (SELECT Name_of_Student, regd, 
            Name_of_exam, SUM(Mark_score) AS TOTALSCORE 
          FROM cixexam, (SELECT @auto := 0, 
                @marks := 0) AS init 
              GROUP BY regd 
          ORDER BY TOTALSCORE DESC) t) AS result 
       HAVING (Name_of_exam='First Terminal Exam' OR 
         Name_of_exam='First Term Test')"; 

$myrank = mysql_query($query_myrank, $dbconnect) or die(mysql_error()); 

$i = 0; 
$j = 0; 
$data = array(); 
while($row_myrank = mysql_fetch_assoc($myrank)) 
{ 
    $data[$i] = $row_myrank; 
    if(isset($data[$i - 1]) 
      && $data[$i - 1]['TOTALSCORE'] == $data[$i]['TOTALSCORE']) 
    { 
     $data[$i]['Rank'] = $j; 
    }else{ 
     $data[$i]['Rank'] = ++$j; 
    } 
     $i++; 
} 
foreach($data as $key => $value) 
{ 
    if($value['regd'] == $regd) 
    { 
     echo $value['Rank']; 
    } 
} 
?>  

Answer 1

Distinct比Group By慢。你可以這樣做，不需要同時使用Group By和Distinct，這可能是你想要實現的。

SELECT regd, Roll_no, Name_of_Student, Name_of_exam, 
     TOTALSCORE, Rank 
FROM 
(
    SELECT t.*, IF(@p = TOTALSCORE, @n, @n := @n + 1) AS Rank, @p := TOTALSCORE 
    FROM 
    (
    SELECT regd, Roll_no, Name_of_Student, Name_of_exam, 
      SUM(Mark_score) TOTALSCORE 
    FROM cixexam, (SELECT @n := 0, @p := 0) n 
    WHERE (Name_of_exam='First Terminal Exam' OR Name_of_exam='First Term Test') 
    GROUP BY regd 
    ORDER BY TOTALSCORE DESC 
) t 
) r 

Answer 2

開始與此：

請不要使用mysql_ *函數的新代碼。他們是no longer maintained和社區已經開始the deprecation process。

相反，您應該瞭解準備好的對賬單並使用PDO或MySQLi。如果你不能決定，這篇文章will help to choose。

如果你想了解，here is good PDO tutorial。