self: super:
# Overlay that adds legacy versions of PostgreSQL that are supported by
# PostgREST.
{
  # PostgreSQL 9.6 was removed from Nixpkgs with
  # https://github.com/NixOS/nixpkgs/commit/757dd008b2f2926fc0f7688fa8189f930ea47521
  # We pin its parent commit to get the last version that was available.
  postgresql_9_6 =
    let
      rev = "571cbf3d1db477058303cef8754fb85a14e90eb7";
      tarballHash = "0q74wn418i1bn5sssacmw8ykpmqvzr0s93sj6pbs3rf6bf134fkz";
      pinnedPkgs =
        builtins.fetchTarball {
          url = "https://github.com/nixos/nixpkgs/archive/${rev}.tar.gz";
          sha256 = tarballHash;
        };
    in
    (import pinnedPkgs { }).pkgs.postgresql_9_6;
}