根据另一列的优先级选择值Oracle SQL

Question

I would like to select only one email address per id , if the id has both a work and personal email, I would only like to display the work email.

with emails as(
select '1' id, 'work' email_type, 'abc@gmail.com' email from dual union all
select '2' id, 'work' email_type, '123@yahoo.com' email from dual union all
select '2' id, 'personal' email_type, '456@msn.com' email from dual union all
select '3' id, 'personal' email_type, 'test@work.com' email from dual
)

For this example I would like to display:

id    email_type    email
1     work          abc@gmail.com
2     work          123@yahoo.com
3     personal      test@work.com

Answer 1

You can prioritize those values in row_number and get the first row for each id.

select id,email_type,email
from (select id,email_type,email
      ,row_number() over(partition by id order by case when email_type='work' then 1 else 2 end) as rn
      from emails) t
where rn = 1

Answer 2

Assuming only possible value for email_type are work and personal, you can use window function row_number :

select *
from (
    select t.*,
        row_number() over (
            partition by id order by email_type desc
            ) as seqnum
    from emails t
    ) t
where seqnum = 1;

Answer 3

You can use a subquery to figure out if there is a work email or not. With your sample data, you can use the MAX function to return the "work" type if it exists, and if it doesn't it will just return "personal". Joining back on that will give the appropriate result.

WITH T1 AS (SELECT id, MAX(email_type) AS e_type FROM table_name GROUP BY id)
SELECT T1.id, T1.e_type, T2.email
FROM T1 LEFT JOIN table_name T2 ON T1.id = T2.id AND T1.e_type = T2.email_type
ORDER BY T1.id