Select from one table if present,else select from another having latest date

There are Three tables T1 and T2 and T3

T3 stores person details T1 stores primary phone number of person, T2 stores non primary phone number of persons.

T1

Personid	Primaryphone	dateload
1	1001	02/08/21
2	1002	03/07/21
4	1004	04/08/20
5	1005	08/09/20

T2

Personid	NonPrimphone	dateload
1	1011	12/03/21
3	1003	20/02/21
4	1024	30/12/21
6	1006	08/08/20
3	1007	04/04/21
3	1008	21/08/21

T3

Per_numb	person_id
501	1
502	2
503	3
504	4
505	5
506	6

What i want is, select all personumber from T3 and thier phone number , the criteria is , if the person is having primary phone number select that, if not having primary phone number select phone number from non primary table having latest dateload.

i.e

O/p

Per_numb	phonenumber
501	1001
502	1002
503	1008
504	1004
505	1005
506	1006

I also want to join these three tables and not use sub queries as the sub query is making the execution slow.

Answer

One method uses coalesce():

select t3.*,
       coalesce( (select t1.primaryphone
                  from t1
                  where t1.personid = t3.personid
                 ),
                 (select t2.phone
                  from t2
                  where t2.personid = t3.personid
                  order by t2.dateload desc
                  fetch first 1 row only
                 )
               ) a_good_phone
from t3;