How to use PDO to update the database?

1) Write the regular update statement and again, instead of values, assign the named placeholders. For example:

$sql = "UPDATE `users`
SET `city`= :city, `phone` = :tel
WHERE `id` = :id";

2) Prepare the query:

$query = $dbh->prepare($sql);

3) Bind the parameters:

$query -> bindParam(':city', $city, PDO::PARAM_STR);
$query -> bindParam(':tel' , $tel , PDO::PARAM_INT);
$query -> bindParam(':id' , $id , PDO::PARAM_INT);

4) Define the bound values:

$tel = '06901234567';
$city = 'New Delhi';
$id = 1;

5) Execute the query:

$query -> execute();

6) Check that the query has been performed and that the database has been successfully updated.

if($query -> rowCount() > 0)
{
$count = $query -> rowCount();
echo $count . " rows were affected.";
}
else
{
echo "No affected rows.";
}
All together now:
$sql = "UPDATE users
SET `city`= :city, `phone` = :tel
WHERE `id` = :id";
$query = $dbh->prepare($sql);
$query -> bindParam(':city', $city, PDO::PARAM_STR);
$query -> bindParam(':tel' , $tel , PDO::PARAM_INT);
$query -> bindParam(':id' , $id , PDO::PARAM_INT);
$tel = '02012345678';
$city = 'London';
$id = 1;
$query -> execute();
if($query -> rowCount() > 0)
{
$count = $query -> rowCount();
echo $count . " rows were affected.";
}
else
{
echo "No affected rows.";
}