SQL Server 2017

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create table tablename (id int, name varchar(20), family varchar(20), phone_number varchar(10));
insert into tablename (id, name, family, phone_number) values
(1, 'A' , 'B', '123456') , (2, 'c' , 'd', '321456'), (3, 'A' , 'B', null), (4, 'A' , 'B', '456789')
4 rows affected

select * from tablename


id
name
family
phone_number


1
A
B
123456

2
c
d
321456

3
A
B
null

4
A
B
456789


delete t from tablename t
where exists (
  select 1 from tablename 
  where name = t.name and family = t.family and id < t.id 
)
2 rows affected

select * from tablename


id
name
family
phone_number


1
A
B
123456

2
c
d
321456