# Return a list of the indices of all occurrences (including overlapping occurrences)
create or replace function string_positions(haystack, needle) as (
  WITH RECURSIVE etc AS (
    SELECT
      position(needle IN haystack) AS start_pos,
      0 as s
    UNION ALL
    SELECT
      position(needle IN substr(haystack, start_pos + 1)) + start_pos AS start_pos,
      start_pos as s
    FROM etc
    WHERE start_pos != s
  )
  SELECT coalesce(array_agg(start_pos order by start_pos),[]::BIGINT[])
  FROM etc
  WHERE start_pos > 0 and s != start_pos
);