Parser - Query Analyser

Hello guys,

My name is Michail Giannakopoulos and I am a graduate student at University
of Toronto. I have no previous experience in developing a system like
postgreSQL before.

What I am trying to explore is if it is possible to extend postgreSQL in
order to accept queries of the form:

Select function(att1, att2, att3) AS output(out1, out2, ..., outk) FROM
[database_name];

where att1, att2, att3 are attributes of the relation [database_name] while
output(out1, out2, out3) expresses the output that comes from 'function'
and the fields that this output should have are (out1, out2, out3). What I
mean is that this kind of query should return tuples that obay to the
'output(...)' schema and are produced by processing the original tuples of
'database_name' relation in attributes att1, att2 and att3.

From what I have seen I need to teak both the parser and the query analyser
in order to accept this form of query. However, I do not know how to tweak
these systems. Even worse I do not know where to begin from.

The manual of extending SQL did not helped me and currently I am debugging
postgreSQL source code. I would appreciate if you could provide me with
more resources and correct ways of how to hack inside postgreSQL files and
system. For example, where do I add a new parse node, where should I change
the the grammar.

Thank you very much for all your time and all your help,
Michail