Example of dynamic queries inside plpgsql stored procedures

dynamic_query_inside_sproc.sql

CREATE TABLE IF NOT EXISTS sample_table (
    id serial,
    field1 text,
    field2 int,
    field3 date
);

INSERT INTO sample_table (field1, field2, field3)
SELECT
    md5(random()::text),
    (random() * 1000)::int,
    now() - (((random() * 1000)::int - (random() * 1000)::int) || ' days')::interval 
FROM generate_series(1, 1000);

CREATE OR REPLACE FUNCTION sample_stored_procedure (
    _order_field text = 'id',
    _order text = 'ASC',
    _limit int = 10,
    _offset int = 0
) RETURNS SETOF sample_table AS $$
DECLARE
    sql text := 'SELECT * FROM sample_table';
BEGIN
    IF _order NOT IN ('ASC', 'DESC') THEN
        _order := 'ASC';
    END IF;
    
    IF _order_field NOT IN ('id', 'field1', 'field2') THEN
        _order_field := 'id';
    END IF;
    
    sql := sql || ' ORDER BY ' || _order_field || ' ' || _order;
    
    IF _offset < 0 THEN
        _offset := 0;
    END IF;
    
    IF _limit < 1 OR _limit > 1000 THEN
        _limit := 10;
    END IF;

    sql := sql || ' LIMIT $1 OFFSET $2';
    
    RETURN QUERY EXECUTE sql USING _limit, _offset;
END
$$ LANGUAGE plpgsql;

SELECT * FROM sample_stored_procedure();

SELECT * FROM sample_stored_procedure('field1');

SELECT * FROM sample_stored_procedure('field1', 'DESC');

SELECT * FROM sample_stored_procedure('field2', 'ASC', 5);

SELECT * FROM sample_stored_procedure('field2', 'ASC', 5, 5);

Relevant parts of documentation http://www.postgresql.org/docs/9.4/static/plpgsql-statements.html (40.5.4)