MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

select @@version;


@@version


8.0.30


create table t(id int, timeline varchar(100));
insert into t values(1,'BASELINE'),(1,'MIDTIME'),(1,'ENDTIME'),
(2,'BASELINE'),(2,'MIDTIME'),(3,'BASELINE'),(4,'BASELINE'),
(5,'BASELINE'),(5,'MIDTIME'),(5,'ENDTIME'),
(6,'MIDTIME'),(6,'ENDTIME')

Records: 12  Duplicates: 0  Warnings: 0


SELECT * FROM t f1
where not exists
(select 1 from t f2 where f1.id=f2.id and timeline not in ('BASELINE','MIDTIME'))


id
timeline


2
BASELINE

2
MIDTIME

3
BASELINE

4
BASELINE


select * from t t1
where 
timeline in ('BASELINE','MIDTIME') and
exists(select 1 from t t2 where t1.id=t2.id and timeline in ('BASELINE','MIDTIME')
group by t2.id having count(distinct timeline)=2)


id
timeline


1
BASELINE

1
MIDTIME

2
BASELINE

2
MIDTIME

5
BASELINE

5
MIDTIME