使用这些代码,我会回复Rank
等于regd
的学生$regd
。实际上,这是一个有效的代码。但是,朋友告诉我,在mysql语句Distinct
和Group By
中不应该一起使用。但作为一个新手,我无法弄清楚如何在不使用Distinct
的情况下实现它,因为它不返回没有Distinct
的行。谁能建议我如何改进这些代码?
<?php
mysql_select_db($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'];
}
}
?>
答案 0 :(得分:1)
Distinct
比Group By
慢。你可以在不使用Group By
和Distinct
的情况下这样做,这可能是你想要实现的目标。
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
答案 1 :(得分:0)
从这开始:
请不要将mysql_ *函数用于新代码。它们是no longer maintained,社区已经开始the deprecation process。
相反,您应该了解准备好的语句并使用PDO或MySQLi。如果您无法决定,请撰写本文will help to choose。
如果您想学习here is good PDO tutorial。