how to select the second row if the first row in empty

Question

how to select the second row in Sql server query if the first row is empty. I have 3 tables

1. Users
2. sites
3. siteUser

A user can be assigned to multiple sites and a site can have multiple users but now i want to get only one user for each site but if the first user doesn't have a mobile number that start with +01 i have to get the second user assigned to that site but him also if he doesn't have i have to select the 3rd. please help

Answer 1

This query gives first registered user with phone number starts with +01 for each site

select s.name, u.*
from site s
outer apply (
                select top(1) * 
                    from user u 
                    where u.phone like '+01%' 
                    and u.id in (select userId FROM siteUser su WHERE su.SiteId = s.Id)
                    order by u.registrationDate
            ) as u