Time overlaps from Nesting queries - sql

Question

Based on the current schema I have been asked to find
-- people who were untested and exposed to some one infectious
-- Do not list anyone twice and do not list known sick people
-- Exposed = at the same place, and overlap in time (No overlap time needed for simplicity)
From the query below I find my answer except I cannot remove the people who are 'postive' because the second part my query i.e the time lapse depends on the first part i.e the time the positive people went to the same locations.
select * from (
select DISTINCT person.PersonID, Register.LocID, Register.Checkin, Register.CheckOut
from person
join Register on Person.PersonID = Register.PersonID
join testing on person.PersonID = testing.PersonID
where testing.Results is 'Positive' ) a
join (
SELECT DISTINCT Person.PersonID, Register.LocID , Register.Checkin, Register.CheckOut
from person join Register on Person.PersonID = Register.PersonID
where person.PersonID
not in (SELECT DISTINCT testing.PersonID from testing)) b on a.LocID = b.LocID
and b.checkin >= a.CheckIn and b.CheckIn <= a.CheckOut
So my question is, What modification does this query need to show the results of the results of the second part only?
I consider the first part to be
select * from (
select DISTINCT person.PersonID, Register.LocID, Register.Checkin, Register.CheckOut
from person
join Register on Person.PersonID = Register.PersonID
join testing on person.PersonID = testing.PersonID
where testing.Results is 'Positive' ) a
And the second part to be
join (
SELECT DISTINCT Person.PersonID, Register.LocID , Register.Checkin, Register.CheckOut
from person join Register on Person.PersonID = Register.PersonID
where person.PersonID
not in (SELECT DISTINCT testing.PersonID from testing)) b on a.LocID = b.LocID
and b.checkin >= a.CheckIn and b.CheckIn <= a.CheckOut

Answer 1

For readability you can create CTEs like this:
with
-- returns all the untested persons
untested as (select p.* from person p left join testing t on t.personid = p.personid where t.testingid is null),
-- returns all the infected persons
infected as (select * from testing where results = 'Positive'),
-- returns all the locids that infected persons visited and the start and dates of these visits
loc_positive as (
select r.locid, i.timestamp startdate, r.checkout enddate
from register r inner join infected i
on i.personid = r.personid and i.timestamp between r.checkin and r.checkout
)
-- returns the distinct untested persons that visited the same locids with persons tested positive at the same time after they were tested
select distinct u.*
from untested u
inner join register r on r.personid = u.personid
inner join loc_positive lp on lp.locid = r.locid
where lp.startdate <= r.checkout and lp.enddate >= r.checkin

Answer 2

This is a complicated query. Because you do not want duplicates, I am going to suggest exists with the outer query just using persons.
The idea to get people in the same place at the same time is a self-join on register using both location and time overlaps. I think that is the most complex part of the query. The rest is checking if a person is or is not positive:
select p.*
from person p
where not exists (select 1
from testing t
where t.personid = p.personId and t.results = 'positive'
) and
exists (select 1
from register r1 join
register r2
on r1.locid = r2.locid and
r1.checkin < r2.checkout and
r2.checkout > r1.checkin join
testing t2
on r2.personid = t2.personid and
t2.results = 'positive' and
t2.timestamp < r2.checkout
where r1.personid = p.personid
);
The timing is a little tricky, but I think the timing makes sense. Someone needs to test positive before they are in the same place. Of course, you can remove the t2.timestamp < r2.checkout if there is no timing constraint.

Answer 3

The solution to this answer was to add a distinct and a column name to the star in the first line.
select DISTINCT unt.PersonID from (
select person.PersonID, Register.LocID, Register.Checkin, Register.CheckOut
from person join Register on Person.PersonID = Register.PersonID join testing on person.PersonID = testing.PersonID
where testing.Results is 'Positive' ) pos
join (
SELECT Person.PersonID, Register.LocID , Register.Checkin, Register.CheckOut
from person join Register on Person.PersonID = Register.PersonID where person.PersonID
not in (SELECT testing.PersonID from testing)) unt on pos.LocID = unt.LocID
and unt.checkin >= pos.CheckIn and unt.CheckIn <= pos.CheckOut;