使用where子句刪除行

Question

我有一個表名論壇， 表看起來像這樣;

id  studentid description teacherid 
1  abc123   hi   zxc123 
2  abc123  hello   qwe321 

我想刪除一行， 是我的嘗試是，

<?php 

require_once('Connections/dbcon.php'); 

mysql_select_db("school", $dbcon); 

$student_id=$_GET['student_id']; 
$delete=mysql_query("DELETE from forum WHERE student_id='$student_id'")or die(mysql_error()); 

echo "<script language='Javascript'>alert('The Forum Successfully Deleted!'); 

location.href='tviewforum.php'</script>"; 
?> 

我想在一個論壇的具體消息。如果一個學生做2個論壇，我想刪除其中1，並保持其他1.

Answer 1

可以保留最大的ID時，有一個學生創建

你可以使用超過1個論壇group by和having獲取最大ID並刪除其他行。

delete T from Table1 T 
join (select max(id) as id , studentid 
     from Table1 
     where studentid ='abc123' 
     group by studentid 
     having count(*) >1 
    ) NewT 
on T.id <> NewT.id 
AND T.studentid = NewT.studentid