Oracle 18c

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create table test (cust_id number, cover1 varchar2(10), cover2 varchar2(10), cover3 varchar2(10));
Insert into test values (1234 , 'PAG' , Null , 'TDE');

1 rows affected

Insert into test values (5678,  Null ,  'GAP' ,  Null);
1 rows affected

select cust_id, cover1 AS cover from test where cover1 IS Not Null
UNION ALL
select cust_id, cover2 AS cover from test where cover2 IS Not Null
UNION ALL
select cust_id, cover3 AS cover from test where cover3 IS Not Null


CUST_ID
COVER


1234
PAG

5678
GAP

1234
TDE


SELECT CUST_ID, COVER FROM(
SELECT * FROM test
UNPIVOT(
   COVER
    for COVER_C
    IN(
     COVER1,
     COVER2,
     COVER3
    )
));


CUST_ID
COVER


1234
PAG

1234
TDE

5678
GAP