Dynamic column in SELECT statement postgres

Question

I am quite new to the postgresql.

what is the best way to achieve this?

SELECT get_columns() 
  FROM table_name;

get_columns(

Answer 1

You wont be able to use a function to generate a column list. And I really don't think this is the best way to approach the problem... That said, you can do it with 8.4 like so:

CREATE OR REPLACE FUNCTION dyn(p_name VARCHAR)
RETURNS SETOF RECORD AS
$$
  DECLARE
    p_sql  TEXT;
  BEGIN
   SELECT 'SELECT ' ||
     CASE p_name WHEN 'foo' THEN ' col1, col2, col3, col4 '
      WHEN 'bar' THEN 'col3, col4, col5, col6'
      WHEN 'baz' THEN 'col1, col3, col4, col6' END ||
   ' FROM mytest'
   INTO p_sql;
   RETURN QUERY EXECUTE p_sql;
  END
$$ LANGUAGE 'plpgsql';

Usage would be: SELECT * FROM dyn('foo') AS (one int, two int, three int, four int)

But honestly I'd suggest just making a view for each device.