Question

Although this technique works great for standard columns, I have run into something I don’t understand. I am rewriting results in my query for reporting purposes and need to order by the aliased column ‘PARENT’, like so:

select fun.MODULE_ID
    , fun.FUNCTION_ID
    , COALESCE(fun.parent_function, fun2.function_id) as PARENT
    , fun.DESCRIPTION
    , fun.FUNCTION_PURPOSE
from MODULE_FUNCTION fun
LEFT JOIN MODULE_FUNCTION fun2
    ON fun.function_id = fun2.function_id
    AND fun2.function_id IN (SELECT parent_function FROM MODULE_FUNCTION)
ORDER BY MODULE_ID
    , PARENT
    , FUNCTION_ID

This works great, but my column ‘PARENT_FUNCTION’ and its alias ‘PARENT’ contain nulls. I would like these to be at the bottom. So when I do this:

ORDER BY MODULE_ID
    , case when PARENT is null then 1 else 0 end, PARENT
    , FUNCTION_ID

I get ” Invalid column name ‘PARENT’. “

Any ideas? (Still very new with SQL!)

Answer 1

SQL Server won’t let you use a column alias elsewhere in the query except in an ORDER BY clause (but not in an expression within ORDER BY), so you have to retype the original column definition. For a more in depth explanation of this (much better than I could give) please see this page

try this:

ORDER by MODULE_ID
   , case when COALESCE(fun.parent_function, fun2.function_id) is null then 1 else 0 end
   , FUNCTION_ID