When the value is not found no message is shown - php

Question

I have the following example database:
rfidtags` (`name`, `id`, `gender`, `email`, `mobile`) VALUES
('Alsan', '39EAB06D', 'Male', 'mydigitalnepal#gmail.com', '9800998787'),
('John', '769174F8', 'Male', 'john#email.com', '23456789'),
('Thvhm,b', '81A3DC79', 'Female', 'jgkhkkmanjil#gmail.com', '45768767564'),
And the following code:
<?php
$mysql_host = 'localhost';
$mysql_port = '';
$mysql_user = 'user';
$mysql_pass = 'password';
$mysql_mydb = 'rfidcards';
$con = new mysqli($mysql_host, $mysql_user, $mysql_pass, $mysql_mydb );
if ($con -> connect_errno) {
echo "Failed to connect to MySQL: " . $con -> connect_error;
exit(2);
}
//$tagid = '39EAB06D';
$tagid = 'CCCCCCCC';
$query = "SELECT name, id FROM rfidtags WHERE id = '$tagid'";
if ($stmt = $con->prepare($query)) {
$stmt->execute();
$stmt->bind_result($name, $id);
$stmt->fetch();
// debug init
//var_dump($stmt);
// debug end
echo "$name $id\n";
$stmt->close();
} else {
echo "failed to fetch data\n";
}
$con->close();
Tags
tagid = '39EAB06D'
and
tagid = 'CCCCCCCC'
are for testing purposes.
When the first is selected, the ressult is shown, but when the second (non existant on the database) is selected, a blank line is shown, instead of "failed to fetch data"

Answer 1

Your echo "failed to fetch data\n"; is in the wrong place. $con->prepare($query) will only return false if there was something wrong in preparing the statement not if the statement returned no entries.
You would want to do the if check on your fetch like:
if($stmt->fetch()) {
echo "$name $id\n";
} else {
echo "No result returned";
}

Answer 2

mysqli::prepare() does not fail when the query returns zero records. In fact, it's a rather bad practice to check if prepare succeeded or not.
Your code would be much easier if you used PDO instead of mysqli, but if you are willing to suffer with mysqli then the right code to do this kind of thing would be:
<?php
$mysql_host = 'localhost';
$mysql_port = '';
$mysql_user = 'user';
$mysql_pass = 'password';
$mysql_mydb = 'rfidcards';
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$con = new mysqli($mysql_host, $mysql_user, $mysql_pass, $mysql_mydb);
$con->set_charset('utf8mb4'); // always set the charset
//$tagid = '39EAB06D';
$tagid = 'CCCCCCCC';
$query = "SELECT name, id FROM rfidtags WHERE id = ?";
$stmt = $con->prepare($query);
$stmt->bind_param('s', $tagid);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($name, $id);
if ($stmt->fetch()) {
echo "$name $id\n";
} else {
echo "failed to fetch data\n";
}

Answer 3

It's wrong because mysqli::prepare() return mysqli_stmt or false.
Generaly, it return false only when you have a wrong SQL query.
But in your case, you have a correct SQL query even if the id you request does not exist in the table.
So you need to check the results after executing stmt but not the stmt before executing.