Code implementation in php-mysql - php

Question

I am trying to understand the code and I am confused to understand the code at this point below. in the first example I want to fetch data from the database and display them as drop-down list but unfortunately it is not displaying anything, and in the second example everything is working fine (fetching data displaying as the drop-down list) bu the problem is that I cant understand the code in the second example it looks much more complicated than the first example. So I want to correct my first example and after that I can rebuilt the second example based on the first one.
First table is department (ID, persondepartment, Description)
Second table board ( personboard, description)
ps: this is for my project so I dont care about Security
First Example - Not Working
<td>Department</td>
<td>
<select name='persondepartment' ID="dept">
<option ID="0">-- Select Department --</option>
<?php
mysql_connect('localhost', 'data_datab', 'password');
mysql_select_db ("data");
$getalldepartments = "SELECT * FROM department";
WHILE ($viewdepartments = mysql_fetch_array(
$getalldepartments)){
?>
<option ID="<?php echo $viewdepartments['ID'];?>
"> <?php echo $viewdepartments ['persondepartment'] ?></option>
<?php } ?>
</select>
</td>
Second Example - Working
<td>Board</td>
<td>
<?php
mysql_connect('localhost', 'data_datab', 'password');
mysql_select_db ("data");
$sql = "SELECT * FROM board";
$result = mysql_query($sql);
echo "<select name='personboard'>";
while ($row = mysql_fetch_array($result)) {
echo "<option value='" . $row['personboard'] . "'>" . $row['personboard'] . "</option>";
}
?>
</td>

Answer 1

Try to change
$getalldepartments = "SELECT * FROM department";
to:
$getalldepartments = mysql_query("SELECT * FROM department");
and consider to use mysqli instead of deprecated mysql extension.
Correct version with PDO
<td>Department</td>
<td>
<select name="persondepartment" id="dept">
<option value="0">-- Select Department --</option>
<?php
try {
$pdo = new PDO('mysql:host=localhost;dbname=data', 'data_datab', 'password');
} catch (PDOException $e) {
echo '<option value="">' . $e->getMessage() . '</option>';
}
$getalldepartments = $pdo->query("SELECT * FROM department");
while ($viewdepartments = $getalldepartments->fetch(PDO::FETCH_ASSOC)) {
?>
<option value="<?= $viewdepartments['ID']; ?>"><?= $viewdepartments['persondepartment']; ?></option>
<?php
}
?>
</select>
</td>