我有两个表,结果和GP.
|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|
我已经做到了：
<?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>";
?>
有了该代码,我得到了这样的东西：
|Matriculation||MAT111||MAT112||MAT113||MAT114||GP|
|TR/2213234561|
|TR/2213234567|
但是我想要
|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.
解决方法:
您希望执行的操作被称为“数据透视”,其他RDBMS对此具有本机支持,而MysqL则没有(通过设计,因为开发人员认为这种操作属于表示层).
但是,您有几种选择：
>构建一个非常可怕的MySQL查询,以手动执行数据透视操作：
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,则可以使用PHP中的循环结构或MysqL中的预处理语句,自动生成此查询,从而使您的生活稍微容易一些.
>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 = $qry->fetchAll(PDO::FETCH_COLUMN, 0);
>遍历结果,构造上面的sql：
mb_regex_encoding($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,将课程数组作为参数传递：
$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>";
>一次性执行上述操作,以便更改MysqL数据库的结构以更紧密地反映此所需的布局(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
