Ignore null entries in sql - mysql

Question

The example below builds a table that extracts the first two score values by userId and passageId. How can I select only records where each record in the new table contains at least two scores (i.e. ignore records where score2 is null)?
Example
Code:
drop table if exists simon;
drop table if exists simon2;
Create table simon (userId int, passageId int, score int);
Create table simon2 (userId int, passageId int, score1 int,score2 int);
INSERT INTO simon (userId , passageId , score )
VALUES
(10, 1, 2),
(10, 1, 3),
(10, 2, 1),
(10, 2, 1),
(10, 2, 5),
(11, 1, 1),
(11, 2, 2),
(11, 2, 3),
(11, 3, 4);
insert into simon2(userId,passageId,score1,score2)
select t.userId, t.passageId,
substring_index(t.scores,',',1) as score1,
(case when length(t.scores) > 1 then substring_index(t.scores,',',-1)
else null
end
) as score2
from
(select userId,passageId,
substring_index (group_concat(score separator ','),',',2) as scores
from simon
group by userId,passageId) t;
select *from simon2;
This is what I get now:
userId passageId score1 score2
1 10 1 2 3
2 10 2 1 1
3 11 1 1 NULL
4 11 2 2 3
5 11 3 4 NULL
This is what I want:
userId passageId score1 score2
1 10 1 2 3
2 10 2 1 1
4 11 2 2 3

Answer 1

Just add this around your query
Select * from ( ...... ) x where score2 is not null

Answer 2

You have no ordering specifying what score goes into score_1 and score_2, so I'll just use min() and max(). You can then do the logic as:
select s.userid, s.passageid,
max(score) as score_1, max(score) as score_2
from simon s
group by s.userid, s.passageid
having count(*) >= 2;
This doesn't give you exactly the same results for 10/2. However, your results are arbitrary because the group_concat() has no order by. SQL tables represent unordered sets. There is no ordering unless you specify it.
If you want an ordering, then define the table as:
Create table simon (
simonId int auto_increment primary key,
userId int,
passageId int,
score int
);
And then use the simonId column appropriately.