SQL query to set a value if data exist - mysql

Question

Here's the fiddle;
http://sqlfiddle.com/#!2/af8015/9
I've some data, and I want to set
if user and g parameter are in table named cl, result column should
be 1;
if user and g parameter are in table named im, but not in cl, result
column should be -1;
else, result column should be 0
I'm using following query;
select *,
case cl.user_id
when null then -1
when im.user_id then 1
end as result
from im
left join cl on cl.user_id = im.user_id
and cl.id_g = im.id_g
left join user on user.user_id = im.user_id
left join g on g.id_g = im.id_g
But, it returns null for -1, and I couldn't set 0 for the last case.
Expected result table is;
user id - g id - result
1 1 1
1 2 1
1 3 0
1 4 1
2 1 1
2 2 1
2 3 -1
2 4 0
...

Answer 1

I can't see a way of generating the 0 result from your sample data.
I believe your result parameter should be computed like this;
IF (cl.user_id IS NOT NULL and cl.id_g IS NOT NULL, 1,
IF(im.user_id IS NOT NULL and im.id_g IS NOT NULL, -1,0)
) result
And, I think your series of JOIN operations should go like this.
FROM user
LEFT JOIN im ON user.user_id = im.user_id
LEFT JOIN cl ON user.user_id = cl.user_id AND im.id_g = cl.id_g
LEFT JOIN g ON im.id_g = g.id_g
That is, you should lead with the user table. Here's an example: http://sqlfiddle.com/#!2/a5c6ef/1/0
Your result parameter is computed like this:
case cl.user_id
when null then -1
when im.user_id then 1
end as result
null values work strangely. A null value can never compare equal to anything, even another null value, so when null then -1 will never fire. This expression, on the other hand, should work.
case when cl.user_id IS NULL then -1
when im.user_id IS NULL then 1
else 0 end as result