mySQL如果id存在则插入其他发送错误给用户，我可以使用哪个metod？

Question

I like to change my code up a bit and if the int $itemID does not exist the user should trigger $retval die, if $itemID exists the user should proceed with the update of the db.

What method is most suitable?

code:

$upd = "UPDATE booking SET userID ='$userID' WHERE itemID ='$itemID'";

$retval = mysql_query($upd, $con);
if(!$retval){
   die('Could not update data: '.mysql_error());
   } 
echo "Updated data successfully
";

Answer 1

You should check for the number of affected rows, like this:

$upd = "UPDATE booking SET userID ='$userID' WHERE itemID ='$itemID'";

$retval = mysql_query($upd, $con);

if(!$retval || 0 === mysql_affected_rows()) {
   die('Could not update data: '.mysql_error());
}

echo "Updated data successfully
";

Also, as stated in the comment, you should be using mysqli_ or even PDO instead of mysql_, since the latter is seriously outdated.