SQL: Count the entities travelling with the between dates

Suppose your data table name is TRAVELS, create a new table RESULTS with these fields:

xdate as date, primary key
n as integer

Now, try something like this code:

docmd.runsql "delete from RESULTS"
dim TRAVELS as recordset
dim RESULTS as recordset
set TRAVELS= currentdb.openrecordset("TRAVELS" , dbopenforwardonly , dbreadonly)
set RESULTS= currentdb.openrecordset("RESULTS")
RESULTS.index= "primarykey"
dim xdate as date
do while not TRAVELS.eof
    xdate= TRAVELS!date_of_departure
    do while xdate <= TRAVELS!date_of_arrival
        RESULTS.seek "=" , xdate
        if RESULTS.nomatch then
            RESULTS.addnew
            RESULTS!xdate= xdate
            RESULTS!n= 1
            RESULTS.update
        else
            RESULTS.edit
            RESULTS!n= RESULTS!n + 1
            RESULTS.update
        end if
        xdate= dateadd("d" , 1 , xdate)
    loop
    TRAVELS.movenext
loop
TRAVELS.close
set TRAVELS= nothing
RESULTS.close
set RESULTS= nothing