如何添加“删除级联”约束？

Question

在 PostgreSQL 8 中是否可以将ON DELETE CASCADES 添加到下表中的两个外键而不删除后者？

# \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)

两个引用的表格都在下面 - 这里：

# \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)

这里：

# \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)

我还想知道在前一个表中添加 2 个索引是否有意义？

更新：谢谢，而且我在邮件列表中得到了建议，我可以在 1 条语句中管理它，因此无需明确启动交易：

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

Answer 1

多列约束的解决方案：

SELECT
    'ALTER TABLE myschema.' || cl.relname ||
    ' DROP CONSTRAINT ' || con.conname || ',' ||
    ' ADD CONSTRAINT ' || con.conname || ' ' || pg_get_constraintdef(con.oid) || ' ON DELETE CASCADE;'
FROM pg_constraint con, pg_class cl 
WHERE con.contype = 'f' AND con.connamespace = 'myschema'::regnamespace::oid AND con.conrelid = cl.oid

Answer 2

根据@Mike Sherrill Cat Recall 的回答，这对我有用：

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

Answer 3

我很确定您不能简单地将on delete cascade 添加到现有的外键约束中。您必须先删除约束，然后添加正确的版本。在标准 SQL 中，我相信最简单的方法是

• 开始交易，
• 删除外键，
• 用on delete cascade添加外键，最后
• 提交事务

对要更改的每个外键重复此操作。

但是 PostgreSQL 有一个非标准扩展，允许您在单个 SQL 语句中使用多个约束子句。例如

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

如果您不知道要删除的外键约束的名称，您可以在 pgAdminIII 中查找它（只需单击表名并查看 DDL，或者展开层次结构直到看到“约束")，或者你可以query the information schema。

select *
from information_schema.key_column_usage
where position_in_unique_constraint is not null

Answer 4

用法：

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

功能：

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;

注意：此函数不会复制初始外键的属性。 它只需要外部表名/列名，删除当前键并替换为新键。