Update table being returned in PostgreSQL - postgresql

Question

I'm looking for help with a PostgreSQL function that returns a table.
I would like to know if there is a way of updating the table that is being returned.
Here's an example,
create or replace function fn_function()
return table(column01 integer, column02 integer, column03 boolean) as $$
return query
select col1, col2, false
from tableXYZ;
/* how can i update the table, let's say column03 before the function exits */
end
$$ language plpgsql;
Can i give an alias to the table being returned?
The postgre version in use is 9.0.8.
Thx in advance.

Answer 1

Here is a set based solution.
The RETURNS TABLE is just portal to get data out you can't do anything inside the function that defines it. You could create another function and call this one and do things to the result set. However I use a temp table so you can manipulate the data before you send it out.
CREATE OR REPLACE FUNCTION fn_function()
RETURNS TABLE(column01 integer, column02 integer, column03 boolean) AS $$
BEGIN
CREATE TEMP TABLE temp_tableXYZ (column01 integer, column02 integer, column03 boolean) ON COMMIT DROP;
INSERT INTO temp_tableXYZ (column01, column02, column03)
SELECT col1,col2,col3
FROM tableXYZ;
--WHERE filter if you can.
UPDATE temp_tableXYZ
SET col1 = 9999;
RETURN QUERY select column01, column02, column03 from temp_tableXYZ;
END;
$$ LANGUAGE plpgsql;
You can call it using an alias like this:
SELECT * FROM fn_function() as my_table;

Answer 2

Just do a query which returns the values you want. It can be plain sql:
create or replace function fn_function()
returns table (
column01 integer, column02 integer, column03 boolean
) as $$
select col1, col2, col2 > 10
from tableXYZ;
$$ language sql;
In the example above column 3 will be true if col2 > 10 and false otherwise. Another example using a subselect:
create or replace function fn_function()
returns table (
column01 integer, column02 integer, column03 boolean
) as $$
select col1, col2, (select max(col1) > 10 from t where col2 = tableXYZ.col1)
from tableXYZ;
$$ language sql;
Notice that it is not return but returns

Answer 3

To select from table, modify the results of select and pass them as results of a function try something like:
create or replace function fn_function()
returns table (
column01 integer, column02 integer, column03 boolean
) as $$
begin
for rec in select col1, col2, false as col3
from tableXYZ;
loop
rec.col3 := col1 > col2;
return next rec;
end loop;
return;
end
$$ language plpgsql;
Details here.
To select get the results of this function simply
SELECT function_alias.col1, function_alias.col2
FROM fn_function() function_alias;
You can do with this function same things you can do with normal tables.