Oracle 18c

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create table data (field_a varchar(200), field_b varchar(200), field_c varchar(200));
insert into data values('A', '001', 'Alan');
1 rows affected

insert into data values('A', '001', 'Alan Walker');
1 rows affected

insert into data values('A', '001', 'Walker Alan');
1 rows affected

insert into data values('A', '001', 'Alexander AlanJoseph');
1 rows affected

select * from data;


FIELD_A
FIELD_B
FIELD_C


A
001
Alan

A
001
Alan Walker

A
001
Walker Alan

A
001
Alexander AlanJoseph


select field_a, field_b, field_c from
(select distinct d1.*, row_number() over(partition by d1.field_a order by d1.field_c) as rnk from data d1
inner join data d2 on 
(instr(d1.field_c, d2.field_c) > 0)) where rnk=1;


FIELD_A
FIELD_B
FIELD_C


A
001
Alan

FIELD_A	FIELD_B	FIELD_C
A	001	Alan
A	001	Alan Walker
A	001	Walker Alan
A	001	Alexander AlanJoseph