Conditionally use fallback value if value in resultset does not match currently logged in user

I have the php script below to get data from a database and return it to a calendar as part of a booking system. The title field, $row["title"], is actually the username of different people for each booking.

Everything works well, but I want to change things so that each user can only see their own username on the calendar, not each other’s. I want them to see 'booked' instead.

I’m pretty new to php, but my guess is that I need to iterate over the created $data array, changing only the title field if it doesn’t match the logged in user. I’m thinking this would come from this in my login script:

$_SESSION["username"] = $username;     <=== I think this needs to be incorporated into the script and the php loop.

What I am trying to do is replace the title field with ‘booked’ if it doesn’t match the logged in user.

I also need to allow all users to see public entries too, say, unavailable, holiday -- so those title values should always be shown.

<?php
$connect = new PDO('mysql:host=localhost;dbname=xxx', 'xxx', 'xxx');
$data = array();
$query = "SELECT * FROM events ORDER BY id";
$statement = $connect->prepare($query);
$statement->execute();
$result = $statement->fetchAll();
foreach($result as $row)
{
    $data[] = array(
        'id'    => $row["id"],
        'title' => $row["title"],
        'start' => $row["start_event"],
        'end'   => $row["end_event"]
    );
}
echo json_encode($data);
?>

Let's say Mary is logged in. The data array will look like this:

[
    {"id":"365","title":"Kerry","start":"2021-08-19 20:00:00","end":"2021-08-19 20:40:00"},
    {"id":"366","title":"John","start":"2021-08-19 19:00:00","end":"2021-08-19 19:40:00"},
    {"id":"367","title":"Mary","start":"2021-08-20 10:00:00","end":"2021-08-20 10:40:00"},
    {"id":"368","title":"Mary","start":"2021-08-20 12:00:00","end":"2021-08-20 12:40:00"},
    {"id":"369","title":"Betty","start":"2021-08-20 15:00:00","end":"2021-08-20 15:40:00"}
]

But I want to change it to this before sending it to the calendar:

[
    {"id":"365","title":"booked","start":"2021-08-19 20:00:00","end":"2021-08-19 20:40:00"},
    {"id":"366","title":"booked ","start":"2021-08-19 19:00:00","end":"2021-08-19 19:40:00"},
    {"id":"367","title":"Mary","start":"2021-08-20 10:00:00","end":"2021-08-20 10:40:00"},
    {"id":"368","title":"Mary","start":"2021-08-20 12:00:00","end":"2021-08-20 12:40:00"},
    {"id":"369","title":"booked","start":"2021-08-20 15:00:00","end":"2021-08-20 15:40:00"}
]

If the the username in the SESSION is the same as the row's title, then show the title, otherwise show booked.

Extension: To show the title value when it matches the logged in user's name OR if it matches so communal/public strings, pile them all into an IN() condition.

Recommendation:

$sql = "SELECT id,
               IF(title IN (?,'unavailable','holiday'), title, 'booked') AS title,
               start_event AS start,
               end_event AS end
        FROM events
        ORDER BY id";
$statement = $connect->prepare($sql);
$statement->execute([$_SESSION['username']]);
echo json_encode($statement->fetchAll(PDO::FETCH_ASSOC));

If you want this to be a dynamic condition, you can prepare your whitelist array in advance:

$allowTitles = [
    $_SESSION['username'],
    'unavailable',
    'holiday',
];

Then you create the necessary number of placeholders and feed the array to execute().

$placeholders = implode(',', array_fill(0, count($allowTitles), '?'));
$sql = "SELECT id,
               IF(title IN ($placeholders), title, 'booked') AS title,
               start_event AS start,
               end_event AS end
        FROM events
        ORDER BY id";
$statement = $connect->prepare($sql);
$statement->execute($allowTitles);
echo json_encode($statement->fetchAll(PDO::FETCH_ASSOC));

P.S. I share @DarkBee's concern regarding unique names in your db table. Typically you should use ids to avoid any chance of data collisions.