Use of OUT and INOUT Parameters   

SQL and PLPGSQL examples of OUTPUT parameters - return single record

Below are some examples in plain SQL and their outputs.

--returning a single record using SQL
CREATE OR REPLACE FUNCTION fn_sqltestout(param_subject text, 
    OUT subject_scramble text, OUT subject_char text)
   AS
$$
    SELECT  substring($1, 1,CAST(random()*length($1) As integer)), substring($1, 1,1)
    $$
  LANGUAGE 'sql' VOLATILE;
  
SELECT  (fn_sqltestout('This is a test subject')).subject_scramble;

-- Output
 subject_scramble
------------------
 This is a test
 
 SELECT  (fn_sqltestout('This is a test subject')).*;
 --Output
   subject_scramble   | subject_char
----------------------+--------------
 This is a test subje | T
 
--Same function but written in plpgsql
--PLPGSQL example -- return one record
CREATE OR REPLACE FUNCTION fn_plpgsqltestout(param_subject text, 
    OUT subject_scramble text, OUT subject_char text)
   AS
$$
BEGIN
    subject_scramble := substring($1, 1,CAST(random()*length($1) As integer));
    subject_char := substring($1, 1,1);
END;
    $$
  LANGUAGE 'plpgsql' VOLATILE;

SQL OUTPUT parameters - return multiple records

--SQL returning multiple records
CREATE OR REPLACE FUNCTION fn_sqltestmulti(param_subject varchar, 
    OUT test_id integer, 
    OUT test_stuff text) 
    RETURNS SETOF record
   AS
$$
    SELECT test_id, test_stuff 
        FROM testtable where test_stuff LIKE $1;
$$
  LANGUAGE 'sql' VOLATILE;
  
--example
SELECT * FROM fn_sqltestmulti('%stuff%');
--example
--OUTPUT--
 test_id |     test_stuff
---------+--------------------
       1 | this is more stuff
       2 | this is new stuff
	   
	   
--PLPGSQL same using 8.3+ syntax
--OUT takes precendence which is why we prefix the table columns
CREATE OR REPLACE FUNCTION fn_plpgsqltestmulti(
    param_subject varchar, 
    OUT test_id integer, 
    OUT test_stuff text) 
    RETURNS SETOF record
   AS
$$
BEGIN
    RETURN QUERY SELECT t.test_id , t.test_stuff 
        FROM testtable As t 
    WHERE t.test_stuff LIKE param_subject;
END;
$$
  LANGUAGE 'plpgsql' VOLATILE;

INOUT parameters - return multiple records

--INOUT return multiple records SQL
CREATE OR REPLACE FUNCTION fn_sqltestmulti_inout(param_subject varchar, 
    INOUT test_id integer, 
    INOUT test_stuff text) 
    RETURNS SETOF record
   AS
$$
    SELECT $2 + test_id, $3 || test_stuff 
        FROM testtable 
        WHERE test_stuff LIKE $1;
$$
  LANGUAGE 'sql' VOLATILE;
  
--Example
  SELECT * FROM fn_sqltestmulti_inout('%stuff%',1, 'test');

 --OUTPUT
 test_id |    test_stuff
---------------+------------------------
       2 | testthis is more stuff
       3 | testthis is new stuff
			 
--INOUT same function in plpgsql 8.3+
--Note its a little odd to look at -- the INOUT param takes 
--precendence in naming which is why we prefix the table columns
CREATE OR REPLACE FUNCTION fn_plpgsqltestmulti_inout(
    param_subject varchar, 
    INOUT test_id integer, 
    INOUT test_stuff text) 
    RETURNS SETOF record
   AS
$$
BEGIN
    RETURN QUERY SELECT t.test_id + test_id , test_stuff || t.test_stuff  
        FROM testtable As t 
    WHERE t.test_stuff LIKE param_subject;
END;
$$
  LANGUAGE 'plpgsql' VOLATILE;