Here is a way to do it in SQL, for one customer.

    select
       entity_id,
       increment_id,
       customer_is_guest
    from
       sales_flat_order
    where
       increment_id = 101125260
    ;

Outputs:

    +-----------+--------------+-------------------+
    | entity_id | increment_id | customer_is_guest |
    +-----------+--------------+-------------------+
    |   2371223 | 101125260    |                 1 |
    +-----------+--------------+-------------------+

To generate a histogram and understand the percentage of your users which are logged in when checking out.

    select
       if(customer_id, 1, 0) as loggedin,
       count(*)
    from
       sales_flat_order
    where
       created_at > '2018-11-01'
    group by
       1
    order by
       1 desc
    ;

Outputs:

    +----------+----------+
    | loggedin | count(*) |
    +----------+----------+
    |        1 |     1194 |
    |        0 |     1693 |
    +----------+----------+