rawi <only4com(at)web(dot)de> writes:
> The Error was caused because I used UNION in place of UNION ALL.
> I still don't understand why the ARRAY (path) could not be grouped...
Yeah, it's an unimplemented feature --- there's no hashing support for
arrays. I hope to get that done for 8.5. In the meantime you have
to use UNION ALL there. If you really need to eliminate duplicate
rows, you can do that via DISTINCT in the outer query.
regards, tom lane