SELECT distinct rows grouped by column name

Question

I have a scenario where i need to pick the latest Id of an employee . The id can be a varchar or int

id      mail
-------------
1234    xyz@abc.com
5678    xyz@abc.com
C123    xyz@abc.com
C234    def@abc.com

Now, my query result just has to be

id      mail
-------------
5678    xyz@abc.com
C234    def@abc.com

The logic is, If there is an integer against the mail id, the highest integer has to be picked. If there is no integer, the varchar value can be picked.

Tried

select max(id), mail from worker  group by mail

But it picks the varchar value when there is a duplicate mail id.

Answer 1

I would use the isnumeric value and ROW_NUMBER to select the right value.

DECLARE @T TABLE (id VARCHAR(10), mail VARCHAR(100))
INSERT @T VALUES 
    ('1234', 'xyz@abc.com'),
    ('5678', 'xyz@abc.com'),
    ('C123', 'xyz@abc.com'),
    ('C234', 'def@abc.com')

SELECT id, mail
FROM (
    SELECT
        id,
        mail,
        ROW_NUMBER() OVER (
            PARTITION BY
                mail
            ORDER BY
                CASE WHEN ISNUMERIC(id) = 1 THEN CONVERT(INT, id) ELSE 0 END DESC,
                id) AS RowNum
    FROM @T
    ) T
WHERE RowNum = 1

The output yields

id         mail
---------- -------------
C234       def@abc.com
5678       xyz@abc.com

Answer 2

One solution I can think of is:

select MAX(t.id), t.email 
from ( 
   select * from Emails where ISNUMERIC(id) = 1 
      union
   select * from Emails where ISNUMERIC(id) <> 1 and email not in 
                              (select email from Emails where ISNUMERIC(id) = 1)
) as t
group by t.email