Postgres: Rename column if exists

rename_column_if_exists.sql

CREATE OR REPLACE FUNCTION column_exists(
  pschema TEXT, 
  ptable TEXT, 
  pcolumn TEXT)
  RETURNS BOOLEAN AS $BODY$
    -- does the requested table.column exist in schema?
    SELECT EXISTS 
         ( SELECT NULL 
             FROM information_schema.columns 
             WHERE table_name=ptable 
               AND column_name=pcolumn 
               AND table_schema=pschema
         ); 
$BODY$ 
  LANGUAGE SQL stable strict;

CREATE OR REPLACE FUNCTION rename_column_if_exists(
  pschema TEXT, 
  ptable TEXT, 
  pcolumn TEXT, 
  new_name TEXT)
  RETURNS VOID AS $BODY$
BEGIN
    -- Rename the column if it exists.
    IF column_exists(pschema, ptable, pcolumn) THEN
        EXECUTE FORMAT('ALTER TABLE %I.%I RENAME COLUMN %I TO %I;',
            pschema, ptable, pcolumn, new_name);
    END IF;
END$BODY$
  LANGUAGE plpgsql VOLATILE;