限制下拉列表中相同值的输出

Question

$dept = $_POST['dept'];
$sql2 = "SELECT batch FROM $dept";
$result2 = mysql_query($sql2);
echo '<form method="post" id="try2" action="pillar.php">';
echo 'Select Batch: ';
echo '<select name="batch" id="batch">';
while($q = mysql_fetch_assoc($result2))
{
    $batch = $q['batch'];
    echo '<option>'.$batch.'</option>'; 
}
echo '</select><br><br>';
echo '<input type="submit">';

.如何限制数据的输出与使用 select 语句从数据库检索到的值相同？请帮忙！提前致谢！

Answer 1

为什么不对 SQL 查询进行分组？

"SELECT `batch` FROM $dept GROUP BY `batch`";

Answer 2

$sql2 = "SELECT batch FROM $dept GROUP BY `batch`";

GROUP BY 子句将导致所有行按 batch 列进行分组，实际上只为每个 batch 值返回一行。