Re: LEFT OUTER JOINS

Hoosain Madhi <MADHIH(at)vodacom(dot)co(dot)za> writes:
> The fact that I request
> c.c7link in the first part of the query, it returns all c7links from
> tbl_c7links. Ideally I should set this to NULL and then request c.c7links in
> the second part of the query (line9). However the parser complains if I
> replace c.c7link with NULL in line 1.

As a general rule, you should provide the exact error message you are
getting when you post a question like this. "The parser complains"
is pretty unhelpful.

I am guessing that the issue is lack of datatype information in the
first select --- UNION currently takes the first select as determining
the types of all its result columns (which is a bug IMHO, but that's
how it acts at the moment). So try casting the NULL to the proper
datatype, eg if the column is text you want "NULL::text" or
"CAST(NULL AS text)".

regards, tom lane