PHP MySQL PDO duplicates - php

Question

I have the below code, which works perfect. What i want to do is to check the refNo first to see if there are duplicates entries in MySQL. If there is then appear a warning message, otherwise appear a "ok" message. How can i do that with PDO? Any help?
(include("db.php"));
$SQLquery = "INSERT INTO mydatabase (refNo, name)
VALUES ('".$_POST["refNo"]."', '".$_POST["name"]."');";
$STH = $dbc->query($SQLquery);
?>
edit: Hello guys,
i prefer not to add primary keys. Is there any other way?

Answer 1

Set up refNo as a primary key. You could also create it as unique but that defeats the purpose - your reference number appears to be a unique primary identifier. Perfect choice for a primary key.
Further, change your query
try {
$SQLquery = "INSERT INTO mydatabase (refNo, name) VALUES (:refNo, :name)";
$SQLquery = $dbc->prepare($SQLquery);
$SQLquery->bindValue(':refNo', $_POST['refNo']);
$SQLquery->bindValue(':name', $_POST['name']);
$SQLquery->execute();
} catch (Exception $e) {
die("Insert error");
}
$count = $SQLquery->rowCount();
if ($count == 1) {
echo "Record added!";
}
This binds the post value to prevent SQL injection too.
Edit: You could follow this up with $count = $SQLquery->rowCount(); which will be 1 if the insert was successful, as it appears you've edited your question since you posted it for more info.

Answer 2

If you want to do this without using a database level constraint, you'll need to do an extra SELECT statement before inserting into the table. But that gives you no absolute guarantees, as it might be two processes want to insert the same row at the same time and they will still succeed.
-- it'll look a little something like this; I'm not familiar with PDO but the structure should be the same
$selectQuery = "SELECT * FROM mydatabase
WHERE refno = '".$_POST["refNo"]."'";
$res = $dbc->query( $selectQuery );
if( $res->count() > 0 ) {
// this result already exists; show error
}
else {
// this result is new; put the insert query here
}