Question

How can I use:

select * from <some_table>;

in a FUNCTION in Postgres?

Answer 1

CREATE OR REPLACE FUNCTION  my_function() RETURNS INTEGER AS '
   DECLARE
      your_record your_table%ROWTYPE;
   BEGIN

      FOR your_record IN SELECT * FROM your_table  
      LOOP

      --
      -- You can access fields of your table using .
      --    your_record.your_field
        ...
      END LOOP;


   END;
' LANGUAGE 'plpgsql'
STABLE;

or

CREATE OR REPLACE FUNCTION  my_function() RETURNS INTEGER AS '
   DECLARE
      your_record your_table%ROWTYPE;
   BEGIN

      SELECT * INTO your_record FROM your_table;

      --
      -- You can access fields of your table using .
      --    your_record.your_field

   END;
' LANGUAGE 'plpgsql'
STABLE;

---

EDIT:

With join returning a record:

CREATE OR REPLACE FUNCTION  my_function() RETURNS SETOF record AS '
   DECLARE
      your_record record;
   BEGIN
      --
      -- You should specify a list of fields instead of *
      --
      FOR your_record IN SELECT * FROM your_table INNER JOIN ...           
         RETURN NEXT your_record;
      END LOOP;
   END;
' LANGUAGE 'plpgsql'
STABLE;

To use my_function(), you have to specify fields and datatypes:
See details here