For the sake of the example, I'll assume you to have copied the relevant Table to the WordPress DB, to have named it `wp_my_xtra_table` and it to contain 3 columns (id,num_val,str_val).

    function wpse106832_shortcode_demo( $atts ) {
        global $wpdb;
        
        extract( shortcode_atts( array(
            'id' => 1
        ), $atts ) );

        $table_row = $wpdb->get_row(
            'SELECT * ' .
            'FROM ' . $wpdb->prefix . '_my_xtra_table ' .
            'WHERE id = ' . $id, ARRAY_A
        );

        if ( ! empty( $table_row ) ) {
            return '<table><tr>' .
                     '<th>ID</th>' .
                     '<th>Numeric Value</th>' .
                     '<th>String Value</th>' .
                 '</tr>' .
                 '<tr>' .
                     '<td>' . $table_row['id'] . '</td>' .
                     '<td>' . $table_row['num_val'] . '</td>' .
                     '<td>' . $table_row['str_val'] . '</td>' .
                 '</tr></table>';
        } else {
            return '<p>Nothing found.</p>';
        }
    }
    add_shortcode( 'wpse106832', 'wpse106832_shortcode_demo' );

With the above, `[wpse106832 id=3]` will display your third database entry.

**Related Reading**

 - The [Shortcode API][1]
 - [`add_shortcode`][2]
 - The [`WPDB` class][3]


  [1]: http://codex.wordpress.org/Shortcode_API
  [2]: http://codex.wordpress.org/Function_Reference/add_shortcode
  [3]: http://codex.wordpress.org/Class_Reference/wpdb