MySQL: Add a WHERE in a LEFT JOIN

Nakrule :

I have the following table:

SequenceNumber are always a multiple of 10. I would like to get, for a specific cpId, the smallest free sequence number (still in a multiple of 10). For example, for cpId = 1, the smallest available should be 20. For cpId = 2, it should be 10.

I have the following statement to get the smallest available sequenceNumber for all cpId, and I don't know how I can add a WHERE cpId = x inside the statement:

SELECT MIN(t1.sequenceNumber + 10) AS nextID
FROM LogicalConnection t1
   LEFT JOIN LogicalConnection t2
       ON t1.sequenceNumber + 10 = t2.sequenceNumber
WHERE t2.sequenceNumber IS NULL;

DB fiddle: https://www.db-fiddle.com/f/ag67AkFzfwPZEva8bTN7Q3/2#&togetherjs=L9nHb3Uu7O

Thank you for your help!

Gordon Linoff :

You can use lead() to get the next number and then some simple logic:

select cpid,
       (case when min_sn > 10 then 10
             else min(sequenceNumber) + 10
        end)
from (select t.*,
             min(sequenceNumber) over (partition by cpid) as min_sn,
             lead(sequenceNumber) over (partition by cpid order by sequenceNumber) as next_sn
      from t
     ) t
where next_sn is null or next_sn <> sequenceNumber + 10
group by cpid, min_sn;