Simple SQL (Get and Edit Data)

<?php
    // get data or modify data
    function getData($sql){
        $db = new mysqli("localhost", "root", "", "database");
        if($db->connect_errno != 0){
            return $db->connect_error;
        }

        // for modify data:
        // $db->query($sql);

        $result = $db->query($sql);

        if($db->errno != 0){
            $db->close();
            return $db->error;
        }

        // for modify data:
        // return $db->affected_rows > 0 ? true : false;

        $data = ($result->num_rows > 0) ? $result->fetch_all(MYSQLI_ASSOC) : [];
        $db->close();
        return $data;
    }
?>

I have one PHP mysqli function for SELECT and another for INSERT/UPDATE/DELETE. Since they are very similar, should I combine them into one function or keep them separate?