On Sun, Dec 29, 2013 at 8:44 AM, knizhnik <knizh...@garret.ru> wrote: > create function volume(r base_table) returns integer as $$ begin return > r.x*r.y; end; $$ language plpgsql strict stable; > create function volume(r derived_table) returns integer as $$ begin return > r.x*r.y*r.z; end; $$ language plpgsql strict stable;
[...] > Execution plans of first and second queries are very similar. > The difference is that type of r_1 in first query is "base_table". > It is obvious that query should return fixed set of columns, so > > select * from base_table; > > can not return "z" column. > But passing direved_table type instead of base_table type to volume() > function for record belonging to derived_table seems to be possible and not > contradicting something, isn't it? Correct. Postgres chooses a function based on the passed signature. When you specify base_table it will choose volume(base_table) and for base_table it will be volume(derived_table) as well. FYI, there is a common practice to follow the DRY principle with inheritance and polymorphic functions in Postgres. On your example it might be shown like this: create function volume(r base_table) returns integer as $$ begin return r.x*r.y; end; $$ language plpgsql strict stable; create function volume(r derived_table) returns integer as $$ begin return volume(r::base_table) *r.z; end; $$ language plpgsql strict stable; -- Kind regards, Sergey Konoplev PostgreSQL Consultant and DBA http://www.linkedin.com/in/grayhemp +1 (415) 867-9984, +7 (901) 903-0499, +7 (988) 888-1979 gray...@gmail.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
