“Invalid Column Name” error in query with order by case statement and outer select

Question

I am trying to order by a column in an outer select statement using a case statement to determine the fields to order by. For some reason, I cannot use the column created in the outer select. If I try to order by that column without using a case statement then it works. What am I doing wrong?

Pseudocode to illustrate problem:

DECLARE @orderBy varchar(8)
SET @orderBy = 'rating'

SELECT
    CASE
        WHEN rating is not null THEN 1
        ELSE  0
    END as hasRating,
    *
FROM

(SELECT col1, ...) AS table1

LEFT OUTER JOIN

(SELECT col1, rating, ...) AS table2

ON table1.col1 = table2.col2

--causes error "Invalid column name 'hasRating'"
ORDER BY 
    CASE WHEN @orderBy = 'rating' THEN hasRating END DESC,
    CASE WHEN @orderby = 'something else' THEN ...

--works
ORDER BY hasRating desc

Answer 1

Does this throw an error:

ORDER BY 
    CASE WHEN @orderBy = 'rating' THEN CASE WHEN rating is not null THEN 1 ELSE  0 END END DESC,
    CASE WHEN @orderby = 'something else' THEN ...

Seems like the CASE in the ORDER by is evaluated before the alias is available.