我有两个表,result
和gp
。
在result
表中,我有这样的东西:
|id||student_id ||course_code||grade||session ||level||semester|
|1 ||TR/2213234561||MAT111 ||A ||2009/2010||100 ||first |
|2 ||TR/2213234561||MAT112 ||B ||2009/2010||100 ||first |
|3 ||TR/2213234561||MAT113 ||C ||2009/2010||100 ||first |
|4 ||TR/2213234567||MAT111 ||D ||2009/2010||200 ||first |
|5 ||TR/2213234567||MAT112 ||C ||2009/2010||200 ||first |
|6 ||TR/2213234567||MAT113 ||C ||2009/2010||200 ||first |
然后gp
表
|id||student_id ||session ||level||semester||gp |
|1 ||TR/2213234561||2009/2010||100 ||first ||4.2|
|2 ||TR/2213234567||2009/2010||100 ||first ||3.5|
|3 ||TR/2213234561||2010/2011||200 ||first ||4.2|
|4 ||TR/2213234567||2010/2011||200 ||first ||3.5|
我想要的是这样的:
|Matriculation||MAT111||MAT112||MAT113||MAT114||GP |
|TR/2213234561||A ||B ||D ||C ||4.2|
|TR/2213234567||C ||D ||E ||F ||3.5|
课程代码不是恒定的 - 这取决于学生注册的课程
我已经这样做了:
<?php
$rst1 = mysql_query("select distinct course_code from result ", $conn);
echo "<table callspacing='4'>";
echo "<tr>";
echo "<td> Matriculation Number </td>";
$c_code = array();
while ($row = mysql_fetch_array($rst1))
{
$c_code[] = $row['course_code'];
}
foreach($c_code as $c_code)
{
echo "<td>" .$c_code. "</td>";
}
$sql ="SELECT result.student_id,
MAX(CASE WHEN course_code = ' $c_code' THEN grade END) $c_code,
gp.CTC
FROM result
JOIN gp
ON gp.student_id = result.student_id
GROUP
BY student_id";
echo "<td> GP</td>";
$rst = mysql_query("$sql",$conn) or die(mysql_error());
while ($row = mysql_fetch_array($rst))
{
echo "</tr>";
echo "<tr>";
echo "<td>" .$row['student_id']. "</td>";
echo "<td>" .$row[$c_code]. "</td>";
}
echo "<td>" .$row[$c_code]. "</td>";
echo "<td>" .$row['CTC']. "</td>";
echo"</tr>";
echo "</table>";
?>
第一个查询是获取课程代码,因为课程不是常量。
有了这段代码,我得到了这样的东西:
|Matriculation||MAT111||MAT112||MAT113||MAT114||GP|
|TR/2213234561|
|TR/2213234567|
但我想要
|Matriculation||MAT111||MAT112||MAT113||MAT114||GP |
|TR/2213234561||A ||B ||D ||C ||4.2|
|TR/2213234567||C ||D ||E ||F ||3.5|
任何建议或方向将不胜感激。
您希望做的被称为"透视"您的数据,并且是其他一些RDBMS具有本机支持的东西,但MySQL没有(根据设计,因为开发人员认为此类操作属于表示层(。
但是,您有以下几种选择:
-
构造一个相当可怕的MySQL查询来手动执行透视操作:
SELECT student_id AS Matriculation, MAT111, MAT112, gp AS GP FROM gp NATURAL JOIN ( SELECT student_id, grade AS MAT111 FROM result WHERE course_code = 'MAT111' ) AS tMAT111 NATURAL JOIN ( SELECT student_id, grade AS MAT112 FROM result WHERE course_code = 'MAT112' ) AS tMAT112 -- etc. WHERE level = @level AND semester = @semester
如果您选择沿着这条路走下去,您可以通过自动生成此查询来使您的生活稍微轻松一些,使用 PHP 中的循环构造或 MySQL 中的预准备语句。
以下是在 PHP 中执行此操作的一种方法:
获取课程列表:
$dbh = new PDO('mysql:dbname=testdb;host=127.0.0.1', $user, $password); $qry = $dbh->query("SELECT DISTINCT course_code FROM result [WHERE ...]"); $courses = $qry->fetchAll(PDO::FETCH_COLUMN, 0);
遍历结果,构造上述 SQL:
mb_regex_encoding($charset); $columns = mb_ereg_replace('`', '``', $courses); $sql = " SELECT student_id AS Matriculation, `".implode("`,`", $columns)."`, gp AS GP FROM gp"; foreach ($columns as $column) $sql .= " NATURAL JOIN ( SELECT student_id, grade AS `$column` FROM result WHERE course_code = ? ) AS `t$column`"; $sql .= " WHERE level = ? AND semester = ?";
执行 SQL,传入课程数组作为参数:
$qry = $dbh->prepare($sql); $params = $courses; array_push($params, $level, $semester); $qry->execute($params);
输出结果:
echo "<table>"; echo "<tr>"; for ($i = 0; $i < $qry->columnCount(); $i++) { $meta = $qry->getcolumnMeta($i); echo "<th scope='col'>" . htmlentities($meta['name']) . "</th>"; } echo "</tr>"; while ($row = $qry->fetch(PDO::FETCH_NUM)) { echo "<tr>"; foreach ($row as $field) echo "<td>" . htmlentities($field) . "</td>" echo "</tr>"; } echo "</table>";
-
执行上述一次性操作,以便更改MySQL数据库的结构以更紧密地反映此所需布局(转换表后很容易,但可能会影响数据库的其他用途(:
CREATE TABLE StudentGrades (PRIMARY KEY('Matriculation')) SELECT student_id AS Matriculation, MAT111, MAT112, gp AS GP -- etc. as above
或者,您可以创建一个
VIEW
,这是一种基于基础表以这种方式构建的"虚拟表"。 -
在 PHP 中手动透视数据(相对繁琐(。