Erreur en exécutant une requête query()

lorsque j'exécute ce code il affiche le message d'erreur
que le mysqli::query(): Empty query(vide)

<?php

    include('config.php');
    function db_query($database_name, $sql) {

        $sql = str_replace("# ", "", $sql); // basic shield against sql injections
        $sql = str_replace("#' ", "", $sql);

        global $db_connection_type, $db_server_address, $db_user, $db_password;

        switch($db_connection_type) {

            case "odbc":
            $db_connection = odbc_connect($database_name, $db_user, $db_password);
            $result = odbc_exec($db_connection, $sql);
            break;

            case "mysql":
            $db_connection = new mysqli($db_server_address, $db_user, $db_password) or die("Error " . mysqli_error("error in db_connection"));

            if (mysqli_connect_errno()) {
        printf("Connect failed: %s\n", mysqli_connect_error("pproblem in connect data base"));
        exit();
    }

            $result = mysqli_query($db_connection,$sql);
            // ($db_name, $sql, $db_connection);
        }

        return $result;
    }

    function fetch_array($array) {
            //
    global $db_server_address, $db_user, $db_password;
$db_connect = new mysqli($db_server_address, $db_user, $db_password) or die("Error " . mysqli_error("error in db_connection"));
[CENTER]
        global $db_connection_type;

        switch($db_connection_type) {

            case "odbc":
            $result = odbc_fetch_array($array);
            break;

            case "mysql":
            //$result = mysqli_fetch_array($array);
            $result = $db_connect->query($array);
        }

        return $result;
    }

?>

comment corriger ce probléme