tsql : is it possible to do nested case statements in a select?

Question

how do i incorporate a nested if statement in a select clause of a sql query? I know to use case when condition then X else y end but how do you do a nested one in the same fashion for each record in a record set.

if x.boy is not null then 
   x.boy 
else if x.girl is not null
   then x.girl 
else if x.dog is not null 
   then x.dog
else 
    x.cat 

here is my attempt:

SELECT top 10
        id,
        case when x.boy <> NULL then 
            x.boy
        else case when  x.girl <> NULL 
            x.girl
                else case when  x.dog <> NULL 
            x.dog
                else x.cat 

        end as Who 
from house x

is this correct?

Answer 1

Yes. There is nothing wrong with a case within a case.

Although, here is your script, written corectly:

SELECT top 10
    id,
    case
        when x.boy IS NOT NULL then x.boy
        else case
            when x.girl IS NOT NULL THEN x.girl
            else case
                when x.dog IS NOT NULL THEN x.dog
                else x.cat
            end
        end
    end as Who 
from house x

OR

SELECT top 10
    id,
    case
        when x.boy IS NOT NULL then x.boy
        when x.girl IS NOT NULL THEN x.girl
        when x.dog IS NOT NULL THEN x.dog
        else x.cat
    end as Who 
from house x

OR

SELECT top 10
    id,
    coalesce(x.boy, x.girl, x.dog, x.cat) AS Who
from house x

Answer 2

You could simplify this with COALESCE.

SELECT TOP 10 id, COALESCE(x.boy, x.girl, x.dog, x.cat) as Who
    FROM house x