MySQL GROUP BY while keeping certain rows by column content - mysql

Question

There is table with duplicated rows. See rows 1 and 2:
id full_name email status active
1 John Doe john#mail.com ok 1
2 John Doe john#mail.com null 1
3 Ricky Duke rick#mail.com null 1
4 Jane Doe jane#mail.com block 1
I need to select distinct rows, not randomly - one distinct row, but the one that has a 'status' NOT NULL.
My query is:
SELECT full_name, email
FROM `subscribers`
WHERE active = 1 AND (status = 'ok' OR status IS NULL)
GROUP BY email
That query selects distinct rows randomly, without prioritizing 'status' field.
How can i prioritize selection of distinct rows, that has a 'status' NOT NULL, and select ones with NULL only in case there is no rows with 'ok' status is present?

Answer 1

You can use row_number():
select s.*
from (select s.*,
row_number() over (partition by email order by (status is not null) desc) as seqnum
from subscribers s
where active = 1
) s
where seqnum = 1;

Answer 2

You could filter with a correlated subquery that does conditional ordering, and gives a lowest priority to null statuses:
select t.*
from mytable t
where t.id = (
select id
from mytable t1
where
t1.full_name = t.full_name
and t1.email = t.email
and t1.active = t.active
order by status is null, status
limit 1
)
This defines duplicats as records that have the same full_name, email and active. You might want to adapt that to your actual definition of duplicates.
Demo on DB Fiddle:
id | full_name | email | status | active
-: | :--------- | :------------ | :----- | :-----
1 | John Doe | john#mail.com | ok | 1
3 | Ricky Duke | rick#mail.com | null | 1
4 | Jane Doe | jane#mail.com | block | 1

Answer 3

(SELECT full_name, email
FROM `subscribers`
WHERE active = 1 AND status IS NOT NULL
GROUP BY email)
UNION ALL
(SELECT full_name, email
FROM `subscribers`
WHERE active = 1 AND status IS NULL AND
email not in (SELECT distinct email
FROM `subscribers`
WHERE active = 1 AND status IS NOT NULL)
GROUP BY email);