mysqli_select_db still throws error even with no error reporting – similar to #8772

[SoulThy]

Description

Reopening the issue:

Hi, I found this issue while troubleshooting a similar problem such as the one referred in #8772 in my own project.
I saw that the original author experienced errors from mysqli_select_db() when the database did not exist, and solved it by removing MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT.

However, in my case, removing all error reporting did not fix the issue. The same behavior persists — mysqli_select_db() still throws a fatal error instead of returning false, and it stops my script.

The code presents a series of echos for debugging purposes.

My code

database_init.php

<?php

// ini_set('display_errors', 1);
// error_reporting(1);
// mysqli_report(MYSQLI_REPORT_ERROR);

require_once 'database_connection.php';

$queryCreateDB = "CREATE DATABASE $database";

$r = 0;

echo "Im about to select the database: " . $database . "<br/>";
$r = mysqli_select_db($conn,$database);
echo "I just run mysqli_select_db<br/>";

echo "r->" . gettype($r) . "<br/>";
echo "r->" . $r . "<br/>";

if(!$r){
    echo "Did not find database! Creating one!<br/>";

    if($conn->query($queryCreateDB)){
        echo "Finished query! <br/>";
    }
    else{
        die("Database creation failed: " . $conn->connect_error);
    }
}
else{
    echo "A database named " . $database . "has been found!<br/>";
}

$conn->close();
?>

Screenshot from my browser

Looking at the screenshot we can see how the code will terminate right here:

$r = mysqli_select_db($conn,$database);

Extra information

Uncommenting the line:

ini_set('display_errors', 1);

Will show me the following error:

I'm here to provide any additional information. Thanks.

PHP Version

PHP 8.3.6 (cli) (built: Mar 19 2025 10:08:38) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.6, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.6, Copyright (c), by Zend Technologies

Operating System

Ubuntu 24.04.2 LTS

[SoulThy]

Also want to clarify the content of database_connection.php.

<?php
$host = 'localhost';
$user = 'root';
$password = '';
$database = 'post_scriptum_db';

$conn = new mysqli($host, $user, $password);

if ($conn->connect_error) {
    die("Connection to the database failed: " . $conn->connect_error);
}

echo "Connection established!<br/>";
?>

[SoulThy]

Adding

mysqli_report(MYSQLI_REPORT_OFF);

does fix this, the execution flow it is not interrupted and the value gets returned correctly.
Also i should have used

var_dump($r);

instead of

echo "r->" . $r . "<br/>";

since if $r is false it becomes an empty string "".

This said, i guess i should not be using mysqli_select_db to check if a database exists.

It’s probably better to query the INFORMATION_SCHEMA.SCHEMATA table.

$queryCheckDB = "SELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = '$database'";