checking if a database exists - php

Question

The code below works fine except it throws a warning when connecting to a database that does not exist. This works fine in product where errors are off, but I would rather not have errors if I don't need to.
function cpanel_db_connect($dbname) {
// normalize
$dbname = convert_to_slug($dbname);
$dbname = CPANEL_USER . '_' . $dbname;
$dbuser = CPANEL_USER . '_' . CPANEL_DB_USER;
// connnect database
$mysqli = new mysqli(CPANEL_DB_HOST, $dbuser, CPANEL_DB_PASS, $dbname);
if ($mysqli->connect_error) {
return false;
}
return $mysqli;
}

Answer 1

It's not a good practice to suppress warnings/errors using the # sign in PHP. You could accidentally suppress an invalid username or password message and you would never know it.
A more appropriate way of checking if the database exists is creating a new instance of Mysql or Mysqli (without specifying the default database) and executing the following query (similar to Marc B's comment):
SELECT COUNT(*) AS `exists` FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMATA.SCHEMA_NAME='my_database_name'
Then you can check the value of the key exists to see if the database is there or not.
Here's a sample code:
// statement to execute
$sql = 'SELECT COUNT(*) AS `exists` FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMATA.SCHEMA_NAME="my_database_name"';
// execute the statement
$query = $mysqli->query($sql);
// extract the value
$row = $query->fetch_object();
$dbExists = (bool) $row->exists;
It is a bit longer but it's safer.

Answer 2

$mysqli = #new mysqli(CPANEL_DB_HOST, $dbuser, CPANEL_DB_PASS, $dbname);
The above works!

Answer 3

This works, just replace $dbname in this code:
if (empty (mysql_fetch_array(mysql_query("SHOW DATABASES LIKE '$dbname' ")))){
echo "DB does Not exist"; }else{ echo "DB exists!";}

Answer 4

Updating to MYSQLI:
$conn = new mysqli('localhost', 'root', '');
$dbname='test';
if (empty (mysqli_fetch_array(mysqli_query($conn,"SHOW DATABASES LIKE '$dbname'"))))
{
echo "DB not exist<br>";
}
else
{
echo "DB exist<br>";
}

Answer 5

Here's how to connect to DB server without selecting a DB, and only connecting if DB exists:
$mysqli = new mysqli($db_biz['server'], $db_biz['user'], $db_biz['password']);
$query = 'SHOW DATABASES LIKE "' . $db_biz['dbName'] . '"';
$resShowBizDB = $mysqli->query($query);
if ($resShowBizDB->num_rows == 1) { //Found database
$mysqli->select_db($db_biz['dbName']);
if ($mysqli->connect_errno) { //Check for errors
var_dump($mysqli);
echo "Failed to connect to biz database: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
}
$mysqli->set_charset('utf8');
} else { //Didn't find DB
die('<h1>ERROR</h1><p>Found no database</p>');
}