Bagaimana cara menambahkan batasan “pada penghapusan kaskade”?

Dalam PostgreSQL 8, apakah mungkin menambahkan ON DELETE CASCADESkedua kunci asing di tabel berikut tanpa menjatuhkan yang terakhir?

# \d scores
        Table "public.scores"
 Column  |         Type          | Modifiers
---------+-----------------------+-----------
 id      | character varying(32) |
 gid     | integer               |
 money   | integer               | not null
 quit    | boolean               |
 last_ip | inet                  |
Foreign-key constraints:
   "scores_gid_fkey" FOREIGN KEY (gid) REFERENCES games(gid)
   "scores_id_fkey" FOREIGN KEY (id) REFERENCES users(id)

Kedua tabel yang direferensikan di bawah - di sini:

# \d games
                                     Table "public.games"
  Column  |            Type             |                        Modifiers
----------+-----------------------------+----------------------------------------------------------
 gid      | integer                     | not null default nextval('games_gid_seq'::regclass)
 rounds   | integer                     | not null
 finished | timestamp without time zone | default now()
Indexes:
    "games_pkey" PRIMARY KEY, btree (gid)
Referenced by:
    TABLE "scores" CONSTRAINT "scores_gid_fkey" FOREIGN KEY (gid) REFERENCES games(gid)

Dan di sini:

# \d users
                Table "public.users"
   Column   |            Type             |   Modifiers
------------+-----------------------------+---------------
 id         | character varying(32)       | not null
 first_name | character varying(64)       |
 last_name  | character varying(64)       |
 female     | boolean                     |
 avatar     | character varying(128)      |
 city       | character varying(64)       |
 login      | timestamp without time zone | default now()
 last_ip    | inet                        |
 logout     | timestamp without time zone |
 vip        | timestamp without time zone |
 mail       | character varying(254)      |
Indexes:
    "users_pkey" PRIMARY KEY, btree (id)
Referenced by:
    TABLE "cards" CONSTRAINT "cards_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "catch" CONSTRAINT "catch_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "chat" CONSTRAINT "chat_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "game" CONSTRAINT "game_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "hand" CONSTRAINT "hand_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "luck" CONSTRAINT "luck_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "match" CONSTRAINT "match_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "misere" CONSTRAINT "misere_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "money" CONSTRAINT "money_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "pass" CONSTRAINT "pass_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "payment" CONSTRAINT "payment_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "rep" CONSTRAINT "rep_author_fkey" FOREIGN KEY (author) REFERENCES users(id)
    TABLE "rep" CONSTRAINT "rep_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "scores" CONSTRAINT "scores_id_fkey" FOREIGN KEY (id) REFERENCES users(id)
    TABLE "status" CONSTRAINT "status_id_fkey" FOREIGN KEY (id) REFERENCES users(id)

Dan juga saya bertanya-tanya apakah masuk akal untuk menambahkan 2 index'es ke tabel sebelumnya?

UPDATE: Terima kasih, dan saya juga sudah mendapat saran di milis, bahwa saya bisa mengelolanya dalam 1 pernyataan dan karenanya tanpa secara eksplisit memulai transaksi:

ALTER TABLE public.scores
DROP CONSTRAINT scores_gid_fkey,
ADD CONSTRAINT scores_gid_fkey
   FOREIGN KEY (gid)
   REFERENCES games(gid)
   ON DELETE CASCADE;

Saya cukup yakin Anda tidak bisa hanya menambah on delete cascadebatasan kunci asing yang ada. Anda harus membuang kendala terlebih dahulu, lalu menambahkan versi yang benar. Dalam SQL standar, saya percaya cara termudah untuk melakukan ini adalah

• memulai transaksi,
• jatuhkan kunci asing,
• tambahkan kunci asing dengan on delete cascade, dan akhirnya
• melakukan transaksi

Ulangi untuk setiap kunci asing yang ingin Anda ubah.

Tetapi PostgreSQL memiliki ekstensi non-standar yang memungkinkan Anda menggunakan beberapa klausa kendala dalam satu pernyataan SQL. Sebagai contoh

alter table public.scores
drop constraint scores_gid_fkey,
add constraint scores_gid_fkey
   foreign key (gid)
   references games(gid)
   on delete cascade;

Jika Anda tidak tahu nama batasan kunci asing yang ingin Anda jatuhkan, Anda dapat mencarinya di pgAdminIII (cukup klik nama tabel dan lihat DDL, atau perluas hierarki hingga Anda melihat "Kendala"), atau Anda dapat menanyakan skema informasi .

select *
from information_schema.key_column_usage
where position_in_unique_constraint is not null

Didasarkan pada jawaban @Mike Sherrill Cat Recall, inilah yang bekerja untuk saya:

ALTER TABLE "Children"
DROP CONSTRAINT "Children_parentId_fkey",
ADD CONSTRAINT "Children_parentId_fkey"
  FOREIGN KEY ("parentId")
  REFERENCES "Parent"(id)
  ON DELETE CASCADE;

Pemakaian:

select replace_foreign_key('user_rates_posts', 'post_id', 'ON DELETE CASCADE');

Fungsi:

CREATE OR REPLACE FUNCTION 
    replace_foreign_key(f_table VARCHAR, f_column VARCHAR, new_options VARCHAR) 
RETURNS VARCHAR
AS $$
DECLARE constraint_name varchar;
DECLARE reftable varchar;
DECLARE refcolumn varchar;
BEGIN

SELECT tc.constraint_name, ccu.table_name AS foreign_table_name, ccu.column_name AS foreign_column_name 
FROM 
    information_schema.table_constraints AS tc 
    JOIN information_schema.key_column_usage AS kcu
      ON tc.constraint_name = kcu.constraint_name
    JOIN information_schema.constraint_column_usage AS ccu
      ON ccu.constraint_name = tc.constraint_name
WHERE constraint_type = 'FOREIGN KEY' 
   AND tc.table_name= f_table AND kcu.column_name= f_column
INTO constraint_name, reftable, refcolumn;

EXECUTE 'alter table ' || f_table || ' drop constraint ' || constraint_name || 
', ADD CONSTRAINT ' || constraint_name || ' FOREIGN KEY (' || f_column || ') ' ||
' REFERENCES ' || reftable || '(' || refcolumn || ') ' || new_options || ';';

RETURN 'Constraint replaced: ' || constraint_name || ' (' || f_table || '.' || f_column ||
 ' -> ' || reftable || '.' || refcolumn || '); New options: ' || new_options;

END;
$$ LANGUAGE plpgsql;

Sadarilah: fungsi ini tidak akan menyalin atribut kunci asing awal. Hanya membutuhkan nama tabel / nama kolom asing, menjatuhkan kunci saat ini dan menggantikannya dengan yang baru.