如何在同一个表中使用多个UNION

Question

我在从 HTML TABLE 形式的结果表中获取数据时遇到问题。我有一个表结果，其中包含有关学生成绩的信息，其中标记列具有多个值，例如 SA1、SA2、SA3、Mid_term、Final。
所以在这个查询中，我从results table 获取first_name 和marks。
问题是我在SA1 column 下获得了所有分数，但我希望在SA1 Column SA2 marks 下SA2 Column SA3 marks 在SA3 Column 下获得SA1 marks。
我几乎尝试了所有方法，但我无法弄清楚我在做什么。

这是我的代码

echo '<table class = "w3-table">
<tr> 
<td> Name </td>
<td> SA1 </td>
<td> SA2 </td>
<td> SA3 </td>
<td> Mid-term </td>
<td> Final </td>
</tr>
<tr>
';
$q = "(SELECT first_name, marks  FROM results WHERE class = '11th Arts' AND 
subject = 'Arts' AND exam_type = 'SA1' )
     UNION ALL (SELECT  NULL, marks as m1  
FROM results WHERE class = '11th Arts' AND subject = 'Arts' 
AND exam_type = 'SA2' ) 
     UNION ALL (SELECT  NULL, marks as m2  FROM results
 WHERE class = '11th Arts' AND subject = 'Arts' AND exam_type = 'SA3' )
     UNION ALL (SELECT  NULL, marks as m3  FROM results 
WHERE class = '11th Arts' AND subject = 'Arts' AND exam_type = 'Mid-term')
     UNION ALL (SELECT  NULL, marks as m4  FROM results 
WHERE class = '11th Arts' AND subject = 'Arts' AND exam_type = 'Final')";

$r = mysqli_query($dbc, $q)
or die(mysqli_error($dbc));
while($row = mysqli_fetch_assoc($r))
{
    $name = $row['first_name'];
    $marks = $row['marks'];
    $marks1 = $row['m1'];
    $marks2 = $row['m2'];
    $marks3 = $row['m3'];
    $marks4 = $row['m4'];
    echo '<tr>
         <td>' .$name .'</td>
         <td>'. $marks. '</td>
         <td>'. $marks1. '</td>
         <td>'. $marks2. '</td>
         <td>'. $marks3. '</td>
         <td>'. $marks4. '</td>
         </tr>';
}
echo '</table>';
?> 

Answer 1

您可以使用 mySql WHEN CASE 来获得您想要的输出。
试试这个

SELECT first_name,
case when exam_type = 'SA1' then marks end as m1,  
case when exam_type = 'SA2' then marks end as m2,
case when exam_type = 'SA3' then marks end as m3, 
case when exam_type = 'Mid-term' then marks end as m4,  
case when exam_type = 'Final' then marks end as m5 
FROM results
WHERE class = '11th Arts' AND 
subject = 'Arts'

你会被淘汰

$name = $row['first_name'];
$marks = $row['m1'];
$marks1 = $row['m2'];
$marks2 = $row['m3'];
$marks3 = $row['m4'];
$marks4 = $row['m5'];

我想它会对你有所帮助。