— справочник типов бизнес-полей
create table client_data_field(
 field_id   number(10) not null,
 field_name varchar2(100 char) not null
);

insert into client_data_field values(1, 'FIRST_NAME');
insert into client_data_field values(2, 'LAST_NAME');
insert into client_data_field values(3, 'MIDDLE_NAME');
insert into client_data_field values(4, 'BIRTH_DAY');

create table client_data_v(
  client_id   number(38) not null,
  field_id    number(10) not null,
  field_value varchar2(1000 char) not null   
);

insert into client_data_v values(777, 1, 'Иван');
insert into client_data_v values(777, 2, 'Иванов');
insert into client_data_v values(777, 4, to_char(date'1984-01-21','dd.mm.yyyy'));

select ... 
  from client_data bd
  join client_data ln on ln.client_id = bd.client_id and ln.field_id = 1 and ln.field_value = ...
 where bd.field_id = 4
   and bd.field_value = ...;