如果在MySql中退出，则替换为另一列

Question

I have a HTML table having values from Mysql. My HTML table looks like this

-------   ------   ------   ------
 type      name     b_id     Edit
-------   ------   ------   ------
Laptop     mac      E1:23    edit
Desktop    dell     D2:45    edit

I am inserting values from input textboxes for type and name. And a select dropdown for b_id. I can edit each row values by clicking edit and i have a dropdown displaying all my b_id's .

I need to update b_id values so that, if it already exists replace with new delete the old.

For suppose i'l hit edit on Desktop dell row. And i'l select E1:23(which is already mapped for laptop mac ). On saving this, E1:23 should map to desktop dell and previous mapping (laptop mac) should be deleted . I mean it should be empty

My Query

$id = $_REQUEST['id']; // Auto Increment
$b_id = $_REQUEST['b_id']; //b_id from select dropdown on edit
$sql = "SELECT * FROM table_name WHERE b_id='$b_id'";
$rs=parent::_executeQuery($sql);
$rs=parent::getAll($rs);
if($rs) // if b_id already exists
{
    //First empty old b_id which has mapped already
    $sql2 = "UPDATE table_name SET b_id='$b_id' WHERE id='$id'";
    $rs=parent::_executeQuery($sql);
}

So how to empty previous mapped b_id. Not the type and name

Answer 1

If you want to empty the data in b_id, your query should be something like this:

if($rs) // if b_id already exists
{
    //First empty old b_id which has mapped already
    $sql2 = "UPDATE table_name SET b_id='' WHERE b_id='$b_id'";
    $rs=parent::_executeQuery($sql2);
}