How do I combine two rows into one single row by overriding NULL values using MySQL?

Question

I have two rows like this:

id    title            format    region    discs    user_id    origin_id
------------------------------------------------------------------------
1     12 Monkeys       DVD       NULL      NULL     NULL       NULL
2     Twelve Monkeys   NULL      NULL      1        2          1

I want to do a SELECT call that always returns the data when a user_id is not NULL . Here's what the result I am looking for should be:

id    title            format    region    discs    user_id   origin_id
-----------------------------------------------------------------------
2     Twelve Monkeys   DVD       NULL      1        2         1

As you can see, format got filled from id 1 because of NULL on id 2 , but everything else was filled from id 2.

What is the MySQL statement that can do this for me?

Answer 1

For your given data, you can use a left join and coalesce() to prioritize the values:

select coalesce(t.id, t2.id) as id,
       coalesce(t.title, t2.title) as title,
       coalesce(t.format, t2.format) as format,
       coalesce(t.region, t2.region) as region,
       coalesce(t.discs, t2.discs) as discs,
       t.user_id
from t left join
     t t2
     on t2.user_id is null
where t.user_id is not null;