在do-while循环中选择计数中断

Question

Where I work we need to register computers into a database, before we just used pen an paper, but I was asked to create an easier method. So I made a small local homepage.

The computers are registered by a tag and number. The tag combined with the number must be unique, I made this loop that increment the entered number until it finds a free one.

                $checkUnique = openConnection("stationer")->prepare("SELECT COUNT(1) FROM `dator` WHERE `tag_id`=:id AND `tag_number`=:number");

                do{
                    $checkUnique -> bindParam(":number", $_POST['number']);
                    $checkUnique -> bindParam(":id", $_POST['tag']);
                    $checkUnique -> execute();
                    $checkUniqueResult = $checkUnique->fetchColumn();

                    if($checkUniqueResult != 0 && empty($searchTagNumber)){
                        $errors[] = "Non-unique tag and number"; break;
                    }

                    $_POST['number'] = $searchTagNumber == "+" ? $_POST['number']+1 : $_POST['number']-1;

                    if($_POST['number'] <= 0){
                        $errors[] = "The tag number can't be 0 or lower"; break;
                    } 
                }while($checkUniqueResult > 0); 

But for some odd reason, it appear to randomly stop, even if the tag and number isn't unique, with no error messages, and I have no idea what causes it.

Answer 1

You can use an unique key like this:

UNIQUE KEY `computer_key` (`tag`,`number`)

Or change engine MyISAM: mysql two column primary key with auto-increment