(

select 1,20190101,100 union all

select 2,20190103,201 union all

select 3,20190102,300 union all

select 5,20180209,99

), b( user_id, time_stamp, order_id ) as

(

select 1,20190102,101 union all

select 2,20190101,200 union all

select 3,20190103,305 union all

select 4,20190303,900

), c as

(

select a.user_id as user_id_a, a.time_stamp as time_stamp_a, a.order_id as order_id_a,

b.user_id as user_id_b, b.time_stamp as time_stamp_b, b.order_id as order_id_b

from a full outer join b

on a.user_id = b.user_id

), d as

(

select user_id_a, time_stamp_a, order_id_a

from c

where coalesce(time_stamp_b,time_stamp_a) <= time_stamp_a

union all

select user_id_b, time_stamp_b, order_id_b

from c

where time_stamp_b >= coalesce(time_stamp_a,time_stamp_b)

)

select user_id_a as user_id, time_stamp_a as time_stamp, order_id_a as order_id

from d

order by user_id_a