Querying Different Table If First Result is Empty - sql

Question

I'm writing a stored procedure to look in two tables PersonTbl, UserTbl. First search the PersonTbl for an userID and if the userID is there get an email address from the UserTbl and return both. However if the ID is not there then search two other tables (PersonsPendingTbl, UsersPendingTbl) for the ID and email. If the ID is not found once again, return null/nulls. So far this is what I've come up with, but not sure if it's the best way of writing it. Let me know if there's any changes you would recommend;
create PROCEDURE [dbo].[MyNewSP]
#ID VARCHAR(MAX)
AS
DECLARE #userID VARCHAR(50)
DECLARE #Email VARCHAR(100)
DECLARE #currentlyActive CHAR
BEGIN
SELECT
#userID = userTbl.ID ,
#Email = personTbl.EMAIL,
#currentlyActive = 'Y'
FROM
personTbl
INNER JOIN userTbl ON personTbl.person_id = userTbl.person_id
WHERE
( userTbl.ID = #ID )
IF ( #userID != #ID ) --Check to see if null
BEGIN
SELECT #currentlyActive = 'N'
SELECT
upt.ID ,
ppt.EMAIL,
#currentlyActive
FROM
PersonsPendingTbl ppt
INNER JOIN dbo.UsersPendingTbl upt ON ppt.person_id = upt.person_id
WHERE
( upt.ID = #ID )
END
ELSE
BEGIN
SELECT
#userID ,
#Email ,
#currentlyActive
END
END

Answer 1

Make a union of both results, but always pick the first row. If the user is registered as Active AND Inactive, it'll return the Active one:
Select *
from (
SELECT userTbl.ID AS UID, personTbl.EMAIL as email, 'Y' as active
FROM personTbl
JOIN userTbl ON personTbl.person_id = userTbl.person_id
WHERE (userTbl.ID = #ID)
union all
SELECT upt.ID AS UID, ppt.EMAIL as email, 'N' as active
FROM PersonsPendingTbl ppt
INNER JOIN dbo.UsersPendingTbl upt ON ppt.person_id = upt.person_id
WHERE (upt.ID = #ID)) user
limit 0,1

Answer 2

I'm not sure about uniqueness of values between your pending and non-pending table, but this should be close enough to get you going.
select
case
when p.PersonId is null and pp.personPendingId is null then null
else userid
end as userid,
case
when p.PersonId is not null then p.email
when p.PersonId is null and pp.PersonPendingID is not null then pp.email
else null
end as email,
case
when p.PersonId is not null then 'Y'
when p.PersonId is null and pp.PersonPendingID is not null then 'N'
else null
end as CurrentlyActive
from userTbl u
left join PersonTbl p on u.Person_id = p.PersonId
left join userPendingTbl up on u.UserId = up.UserPendingId
left join PersonPendingTbl pp on up.personPendingId = pp.PersonPendingID
where u.UserId = #ID