Simple select query gives error

Question

Does anyone have any idea why I get two errors for such a simple query? Error message are:

Warning: mysqli::prepare(): Couldn't fetch mysqli in (...)/functions.php on line 503

Fatal error: Call to a member function bind_param() on null in (...)functions.php on line 504

$query_select = ("SELECT * FROM vat WHERE vat_status = ?");
$stmt = $mysqli->prepare($query_select); // line 503
$stmt->bind_param("s", $vat_status); 
$stmt->execute();
$stmt->store_result();
$count = $stmt->num_rows();

$stmt->bind_result ($vat_id          ,
                    $vat_rate        ,
                    $vat_account     ,
                    $vat_description ,
                    $vat_status      ,
                    $vat_timestamp   ); 

Answer 1

The problem was that I was triggering an UPDATE statement and then an SELECT statement, and both of them used $stmt variable. That was what went wrong.

Now I use

mysqli_stmt_close($stmt); 

Which really closes the $stmt and frees the result, so I can trigger after an update, the select statement.