Question

In a plpgsql function, I have a variable of type record:

my_rec RECORD;

This record contains a row from an arbitrary table, so I do not know the columns before it is executed.
However, I do have the name of at least one of the columns available as a varchar.

The question is: How do I retrieve the value for a given column from my_rec?

Answer 1

Use hstore to work with records with dynamic columns in PL/PgSQL functions:

CREATE EXTENSION hstore;

CREATE OR REPLACE FUNCTION test_fn(col_name text) RETURNS text AS $$
DECLARE 
  input_row record;
  col_value text;
BEGIN
  SELECT INTO input_row 
    * 
  FROM ( VALUES ('a','b','c',1) ) AS dummyrow(col1,col2,col3,intcol);

  SELECT INTO col_value
    hstore(input_row) -> col_name;

  RETURN col_value;
END;
$$ LANGUAGE 'plpgsql';

hstore is an extension, but it’s an extension that’s been bundled with PostgreSQL since 8.3 and has been installable using CREATE EXTENSION since 9.1. The record-to-hstore conversion has been supported since something like 8.4 or 9.0.