Postgresql aggregate function for tsvectors

tsvector_agg.sql

CREATE OR REPLACE FUNCTION concat_tsvectors(tsv1 tsvector, tsv2 tsvector)
RETURNS tsvector AS $$
BEGIN
  RETURN coalesce(tsv1, to_tsvector('default', ''))
      || coalesce(tsv2, to_tsvector('default', ''));
END;
$$ LANGUAGE plpgsql;

CREATE AGGREGATE tsvector_agg (
  BASETYPE = tsvector,
  SFUNC = concat_tsvectors,
  STYPE = tsvector,
  INITCOND = ''
);