Re: recursive query crash

Gregory Stark <stark@enterprisedb.com> writes:
> This crashes, apparently it tries to look up the result type on a NULL
> planstate:
> with recursive  z(i) as (
>     select * 
>       from t 
>      union all 
>       (with a(i) as (select  * from z) 
>     select * from a)
>     )
>  select * from z;

Hmm ... I tried to fix this by changing the order in which the subplans
get initialized, but that just moves the crash to the other subplan.
The problem really is that what we have here is two mutually recursive
WITH entries, and neither one can be successfully initialized in the
executor before the other one is.  I begin to see why the SQL spec
forbids this syntax altogether.

I'm inclined to prevent this case by forbidding recursive references
inside nested WITH clauses.  Thoughts?
        regards, tom lane