create table channels
(channel_id int, 
channel_name varchar(10),
channel_start_dt date,
channel_end_dt date);
insert into channels(channel_id, channel_name, channel_start_dt, channel_end_dt) values
(53, "Agent 1", "2018-01-01", "9000-12-31"),
(54, "Agent 2", "2018-01-01", "2019-12-31"),
(55, "Agent 3", "2019-06-01", "9000-12-31"),
(56, "Agent 4", "2020-01-17", "9000-12-31"),
(57, "Agent 5", "2020-01-22", "9000-12-31"),
(87, "Agent 17", "2019-08-01", "2020-01-25");

delimiter // ;
create procedure procedure1()
begin

create temporary table intervals
(
start date,
end date);

create temporary table crjoin
(st1 date,
end1 date,
st2 date,
end2 date);

create temporary table results
(st date,
end date,
l int);

insert into intervals 
(select channel_start_dt, channel_end_dt
from channels);

select @k := 1;

while (@k != 0) do

insert into crjoin
(select c.*, h.*
from intervals c
join intervals h
on 1=1);

insert into results
(select
case
  when (st2 < end1 and st2 >= st1 and end2 > end1) then st1
  when (st2 < st1 and end2 > st1 and end2 <= end1) then st2
  when (st2 <= st1 and end1 <= end2)  then st2
end st,
case
  when (st2 < end1 and st2 >= st1 and end2 > end1) then end2
  when (st2 < st1 and end2 > st1 and end2 <= end1) then end1
  when (st2 <= st1 and end1 <= end2)  then end2
end end,
case
  when (st2 < end1 and st2 >= st1 and end2 > end1) or (st2 < st1 and end2 > st1 and end2 <= end1) or (st2 <= st1 and end1 <= end2) or (st2 >= st1 and end1 >= end2)
  then 1
  else 0
end l
from crjoin);

truncate table intervals;
truncate table crjoin;

insert into intervals
(
select distinct st, end
from results);

select @k := sum(l) from results;

truncate table results;

end while;

select 
case when (count(start) != 1) then "FALSE"
else "TRUE"
end answer
from intervals;


end; //
delimiter ; //

call procedure1;