Is there any chance to implement polymorphic calls in PostgreSQL?
Consider the following definitions:
create table base_table (x integer, y integer);
create table derived_table (z integer) inherits (base_table);
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;
insert into base_table values (1,2);
insert into derived_table values (3,4,5);
postgres=# select * from base_table;
x | y
---+---
1 | 2
3 | 4
(2 rows)
postgres=# select volume(r) from base_table r;
volume
--------
2
12
(2 rows)
postgres=# select volume(r) from only base_table r union all select
volume(r_1) from only derived_table r_1;
volume
--------
2
60
(2 rows)
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?
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