Common Table expression in a UDF that returns a table

I have an SQL statement I'm trying to turn into a table user defined
function (ie. a UDF that returns a table).

However, this SQL statement uses Common table expressions via the "with
TmpTable as (select ...)"

Which the create function doesn't seem to like.

I've tried replacing the CTE with a "Declare Global Temporary Table TmpTable
as (select ...) with data"

But, I get an error trying to run the create procedure:
SQL0577 - Modifying SQL data not permitted.

I added the "reads SQL data" statement to the UDF, but it doesn't seem to
have helped.  I do not modify any data in this statement.


Anybody know how I need to do this?

Thanks,
Charles