first of all, let me congratulate you on your chapters in “Pro Oracle SQL”., which I’ve read with great interest. I think that analytic functions, and the model clause, are very worthwhile for DBAs to know about.
Would it be okay to ask a question here? I want to use he model clause, with it’s iterate() functionality, to build my own, very simple listagg function (essentially, for learning purposes). As the list may become bigger than 4000 chars, I need to have a clob as the “base case” of the recursion, so I replaced your line

measures (cast (‘ ‘ as varchar2(&&listsize)) cname_list, cname)

with any of the following

measures (cast (to_clob(”) as clob) cname_list, cname)
measures (cast (empty_clob() as clob) cname_list, cname)
measures (to_clob(”) cname_list, cname)

but all result in the same error

ORA-00932: inconsistent datatypes: expected – got CLOB

In fact, the error does not seem to be related to the model clause, as it results from a simple

select cast (‘ ‘ as clob) from dual

too… Would you perhaps have a hint for me what I’m doing wrong here?
Many thanks in advance!
Sigrid