在下拉菜單上限制相同值的輸出

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">'; 

.how可以限制使用select語句從數據庫檢索到的相同值的數據輸出嗎？幫助請！提前致謝！

Answer 1

爲什麼不對你的SQL查詢進行分組？

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

Answer 2

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

的GROUP BY子句將導致所有的行由batch列只有有效返回一行每個batch值進行分組。