Question

I am thinking I am getting close but not sure:

I have an example Table containing email address, Personal and Work.
I am trying to create a new table which holds a single address.

Then insert an email address, example: If a user has a work email but no personal email, the insert work email and if no work email, insert personal email.

The following code does not work but it’s just to show some of the many variations I have used:

USE EXAMPLE_DB

GO

CREATE TABLE USER_EMAIL(
 USER_NBR CHAR(1) NOT NULL
,EMAIL VARCHAR(30)NULL
)

GO

INSERT INTO USER_EMAIL(
 USER_NBR
,EMAIL
)

SELECT USER_NBR
,CASE WHEN EMAIL_ADDR IS NULL AND EMAIL_TYPE = 'Personal' THEN EMAIL_TYPE = 'Work' END EMAIL
,CASE WHEN EMAIL_ADDR IS NULL AND EMAIL_TYPE = 'Work'     THEN EMAIL_TYPE =  'Personal' END EMAIL
FROM EMAIL_DATA

Here is the table for the EMAIL_DATA:

USER_NBR   EMAIL_TYPE       EMAIL_ADDR
1          Personal 
2          Personal     [e-mail]
3          Personal         [e-mail]
4          Personal 
5          Personal         [e-mail]
1          Work         [e-mail]
2          Work         [e-mail]
3          Work 
4          Work         [e-mail]
5          Work 

Thanks everyone!

Answer 1

Here’s an example using row_number:

insert  user_email
        (user_nbr, email)
select  user_nbr
,       mail.email_addr
from    (
        select  user_nbr
        ,       email_addr
        ,       row_number() over (partition by user_nbr
                  order by
                  case 
                  when email_type = 'personal' then 1
                  when email_type = 'work' then 2
                  end) as rn
        from    email_data
        ) usr
where   usr.rn = 1

Since there are just two email types, you could also use left join twice:

insert  user_email
        (user_nbr, email)
select  user_nbr
,       coalesce(pers.email_addr, work.email_addr)
from    (
        select  distinct user_nbr
        from    email_data
        ) usr
left join 
        email_data as pers 
on      pers.user_nbr = usr.user_nbr
        and work.email_type = 'personal'
left join 
        email_data as work
on      work.user_nbr = usr.user_nbr
        and work.email_type = 'work'

Another approach that looks up the preferred email address using cross apply:

insert  user_email
        (user_nbr, email)
select  user_nbr
,       mail.email_addr
from    (
        select  distinct user_nbr
        from    email_data
        ) usr
cross apply
        (
        select  top 1 *
        from    email_data mail
        where   mail.user_nbr = usr.user_nbr
                and mail.email_addr is not null
        order by
                case 
                when email_type = 'personal' then 1
                when email_type = 'work' then 2
                end
        ) mail