Postgresql 如何加上「；“关于删除级联”；约束条件？

在PostgreSQL 8中，是否可以向下表中的两个外键添加

ON DELETE CASCADES

，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)

两个参考表如下-此处：

# \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)

在这里：

# \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两个索引是否有意义

更新：谢谢，而且我在邮件列表中得到了建议，我可以在一条语句中管理它，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;

---

我很确定，您不能简单地将delete cascade上的

添加到现有的外键约束中。必须先删除约束，然后添加正确的版本。在标准SQL中，我认为最简单的方法是


启动交易
放下外键
在delete cascade上添加一个带有
的外键，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，允许您在一条SQL语句中使用多个约束子句。比如说

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

如果不知道要删除的外键约束的名称，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”），也可以

用法：

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。
它只接受外来表名/列名，删除当前键并用新键替换。
根据@Mike Sherrill Cat Recall的回答，这对我来说是有效的：

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

谢谢，我也是这么想的——但是外键怎么办呢？它们只是可以轻松删除和读取的约束（类似于NOTNULL）吗？@AlexanderFarber:是的，它们被命名为约束，可以轻松删除和添加。但您可能希望在事务中这样做。更详细地更新了我的答案。+1用于在pgAdminIII中查找ot。它甚至为您提供了删除约束和添加约束命令，因此您只需复制并粘贴到查询窗口中，然后根据需要编辑命令。编写完查询后，我注意到我的Postgres GUI（Navicat）让我在GUI中轻松地做此更改：对于大型表，如果
无效
并在单独的事务中进行验证，是否可以执行此操作？我对此有点担心，但我注意到您没有在引用列上创建索引（例如，
pref_scores.gid
）。如果引用表中有许多行，则删除这些表将花费很长时间。一些数据库会自动在引用列上创建索引；PostgreSQL让您自己决定，因为在某些情况下它是不值得的。谢谢！实际上，我注意到delete需要很长时间，但不知道这就是为什么外键上的索引不值得使用时会出现这种情况的原因？我将您的发现纳入了我的答案中。（这一条语句也是一个事务。）@AlexanderFarber:您什么时候可以省略FK的引用列上的索引？当有另一个索引不完全匹配时，这将很好地工作（例如，您可能有一个用于频繁相似性搜索的三元索引，这也适用于FK delete）。当删除不频繁且可以安排在非工作时间时。当表频繁更新引用值时。当引用表非常小但经常更新时。异常经常发生，因此PostgreSQL社区更愿意对其进行控制，而不是使其自动化。
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;

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