SELECT DISTINCT PARENT_ID

Question

//select parent_id - display unique value 
<?php 
//database connection 
$con = mysql_connect("xxxx","xxxx","xxxx"); 
if (!$con) { 
    die('Could not connect: ' . mysql_error()); 
} 
mysql_select_db("btreedata", $con); 
//select distinct query 
$query = mysql_query("SELECT DISTINCT parent_id FROM btree"); 
$result = mysql_query($sql); 
//dropdown list 
echo "<select name='parent_id'>"; 
while ($row = mysql_fetch_array($result)) { 
    echo "<option value='".$row[0]."'>".$row[0]."</option>"; 
} 
echo "</select>"; 
?> 

輸出顯示是這樣的：

1000 
1000 
1004 
1004 
1003 
1001 
1005 
1001 

我怎麼能只顯示

1000 
1001 
1003 
1004 
1005 

Answer 1

SELECT parent_id FROM btree group by parent_id order by parent_id ASC