Concatenate

Hi,


can you help me with this tricky concat i have?
I have a function with an execute statement, one line of it doing an md5
hash of some concatenated xml paths with values. I cannot get this one
work, postgres is always complaing about some things, like: "functions
and operators can take at most one set argument"

EXECUTE'
...
md5_hash=md5(unnest(xpath(''/foo/bar'',xml_content::xml))::text) ||
(unnest(xpath(''/foo/bar2'',xml_content::xml))::text)
....


Kind regards,

Frank Jansen