Description:
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From manual page: https://php.net/mysqli.query
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Please replace $result->free instead $result->close(). The close () method for the mysql_result class does not exist.

Example #1 mysqli::query() example
Object oriented style
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...
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if ($result = $mysqli->query("SELECT * FROM City", MYSQLI_USE_RESULT)) {

    /* Note, that we can't execute any functions which interact with the
       server until result set was closed. All calls will return an
       'out of sync' error */
    if (!$mysqli->query("SET @a:='this will not work'")) {
        printf("Error: %s\n", $mysqli->error);
    }
    $result->close();
}

$mysqli->close();