Oracle 18c

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create table test (Id char);
insert into test values('A');
1 rows affected

insert into test values('B');
1 rows affected

insert into test values('C');
1 rows affected

insert into test values('D');
1 rows affected

insert into test values('E');
1 rows affected

SELECT id, PRIOR id AS id2
FROM   test
WHERE  LEVEL = 2
CONNECT BY NOCYCLE PRIOR id > id
ORDER BY id, id2


ID
ID2


A
B

A
C

A
D

A
E

B
C

B
D

B
E

C
D

C
E

D
E