Find people absent from the country for a certain time

Question

I have a table that has the "document number" field, the type of flow (entering or leaving the country), date of birth, and the date the flow occurred.

Knowing that a person can leave or enter several times a year, how can I list those people (by their document number) of legal age (>=21yo) who were out of the country in a specific interval of the year (for example: between May 1, 2021 and August 1, 2021)?

ideally a syntax according to postgresql

EDIT: Info complement

Table: flows

id_flow	doc_number	brth_date	flow_type	flow_date
1	123	1999-05-01	in	2020-06-01
2	123	1999-05-01	out	2020-10-30
3	222	1988-01-09	out	2021-01-01
4	180	1993-11-15	out	2021-06-16
5	222	1988-01-09	in	2021-10-30
6	223	2009-09-05	out	2020-06-04
7	223	2009-09-05	in	2021-12-04

where dates are yyy-MM-DD and should return:

doc_number
123
222

because these people were out in the whole interval and has legal age.

Answer 1

I think , you need sql statement like this:

select distinct person
from
(select person, max(date) as LEAVE_DATE from documentnumber where date<'2021-05-01' and flow='leaving' group by person ) A 
JOIN 
(select person,MAX(date) as ENTER_DATE from documentnumber where date<'2021-08-01' and flow='entering' group by person) B ON A.PERSON=B.PERSON 
where A.LEAVE_DATE>B.ENTER_DATE