PDO update table with existing value? - php

Question

I built PHP 2 year ago and now i want to change all about database to PDO,i have some problem with update table. I use this function to update table.
public function update($tabel, $fild = null ,$where = null)
{
$update = 'UPDATE '.$tabel.' SET ';
$set=null; $value=null;
foreach($fild as $key => $values)
{
$set .= ', '.$key. ' = :'.$key;
$value .= ', ":'.$key.'":"'.$values.'"';
}
$update .= substr(trim($set),1);
$json = '{'.substr($value,1).'}';
$param = json_decode($json,true);
if($where != null)
{
$update .= ' WHERE '.$where;
}
$query = parent::prepare($update);
$query->execute($param);
$rowcount = $query->rowCount();
return $rowcount;
}
everything work fine using this
$updatefild = array('count' => 20);
$where = "id = '123'";
echo $db->update("mytable",$updatefild, $where);
but i get problem when i want to update row with existing row, in mysql_query I usually use
mysql_query("update mytable set count=count+1 where id='123'");
how i achieve that use PDO ?
thanks

Answer 1

First, why are you using JSON just to decode it into an array? That is confusing.
Secondly, if you were trying to add a number to an existing field, you don't even need prepare().
You could just do
PDO->query("update mytable set count=count+".intval($int)." where id='123'");
If you were doing prepare, you could do:
$stmt = PDO->prepare("update mytable set count=count+:count where id='123'");
$stmt->execute(array(':count' => 1));
or
$stmt = PDO->prepare("update mytable set count=count+? where id='123'");
$stmt->execute(array(1));
Edit: You wouldn't be able to do it with how your function is written as you can't bind column names. PDO will quote it as a standard string. You would have to find a work around, possibly including the =count in the field somehow.