MySQL 5.7

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CREATE TABLE logistics (
    id int primary key,
    campaign VARCHAR(255),
    inbound_date VARCHAR(255),
    outbound_date VARCHAR(255)
);

INSERT INTO logistics
(id, campaign, inbound_date, outbound_date)
VALUES 
("1", "C001", "2019-01-01", "2019-02-08"),
("2", "C001", "2019-05-10", "2019-05-12"),
("3", "C001", "2019-06-12", NULL),
("4", "C001", NULL, "2019-06-15"),
("5", "C002", "2019-11-14", "2019-11-22"),
("6", "C002", NULL, "2019-12-13"),
("7", "C002", NULL, NULL);
SELECT campaign,
       coalesce(inbound_date, outbound_date) as event_date
FROM logistics;


campaign
event_date


C001
2019-01-01

C001
2019-05-10

C001
2019-06-12

C001
2019-06-15

C002
2019-11-14

C002
2019-12-13

C002
null


select campaign,
       (case when inbound_date is not null then 'inbound_date' 
             when outbound_date is not null then 'outbound_date'
        end) event_date,
       (case when inbound_date is not null then inbound_date
             when outbound_date is not null then outbound_date
        end) as event_date
from logistics;


campaign
event_date
event_date


C001
inbound_date
2019-01-01

C001
inbound_date
2019-05-10

C001
inbound_date
2019-06-12

C001
outbound_date
2019-06-15

C002
inbound_date
2019-11-14

C002
outbound_date
2019-12-13

C002
null
null

campaign	event_date
C001	2019-01-01
C001	2019-05-10
C001	2019-06-12
C001	2019-06-15
C002	2019-11-14
C002	2019-12-13
C002	null

campaign	event_date	event_date
C001	inbound_date	2019-01-01
C001	inbound_date	2019-05-10
C001	inbound_date	2019-06-12
C001	outbound_date	2019-06-15
C002	inbound_date	2019-11-14
C002	outbound_date	2019-12-13
C002	null	null