为什么 drop table cascade 没有删除 postgresql 中的 child table？

Question

我有以下两个 tables，其架构如下所示：-

postgres=# \d products1;
                               Table "public.products1"
       Column       |  Type   |                       Modifiers
--------------------+---------+--------------------------------------------------------
 id                 | integer | not null default nextval('products1_id_seq'::regclass)
 name               | text    | not null
 default_picture_id | integer |
Indexes:
    "products1_pkey" PRIMARY KEY, btree (id)
    "unique_id_default_pic_id" UNIQUE CONSTRAINT, btree (id, default_picture_id)
Foreign-key constraints:
    "fk_products_1" FOREIGN KEY (id, default_picture_id) REFERENCES product_pictures1(product_id, id) ON UPDATE RESTRICT ON DELETE RESTRICT
Referenced by:
    TABLE "product_pictures1" CONSTRAINT "fk_id_product_id" FOREIGN KEY (id, product_id) REFERENCES products1(default_picture_id, id)


postgres=# \d product_pictures1;
                           Table "public.product_pictures1"
   Column   |  Type   |                           Modifiers
------------+---------+----------------------------------------------------------------
 id         | integer | not null default nextval('product_pictures1_id_seq'::regclass)
 img_path   | text    | not null
 product_id | integer |
Indexes:
    "product_pictures1_pkey" PRIMARY KEY, btree (id)
    "unique_id_productid" UNIQUE CONSTRAINT, btree (id, product_id)
Foreign-key constraints:
    "fk_id_product_id" FOREIGN KEY (id, product_id) REFERENCES products1(default_picture_id, id)
Referenced by:
    TABLE "products1" CONSTRAINT "fk_products_1" FOREIGN KEY (id, default_picture_id) REFERENCES product_pictures1(product_id, id) ON UPDATE RESTRICT ON DELETE RESTRICT

以下两个 table 互相推荐：-

当我尝试删除任何一个 table 时，出现以下错误：-

postgres=# drop table products1;
ERROR:  cannot drop table products1 because other objects depend on it
DETAIL:  constraint fk_id_product_id on table product_pictures1 depends on table products1
HINT:  Use DROP ... CASCADE to drop the dependent objects too.

但是当我用级联选项删除时，table被删除了，但它不会删除另一个table或其在table中的外键列，它只删除外键约束。

postgres=# drop table products1 cascade;
NOTICE:  drop cascades to constraint fk_id_product_id on table product_pictures1
DROP TABLE

postgres=# \d product_pictures1;
                           Table "public.product_pictures1"
   Column   |  Type   |                           Modifiers
------------+---------+----------------------------------------------------------------
 id         | integer | not null default nextval('product_pictures1_id_seq'::regclass)
 img_path   | text    | not null
 product_id | integer |
Indexes:
    "product_pictures1_pkey" PRIMARY KEY, btree (id)
    "unique_id_productid" UNIQUE CONSTRAINT, btree (id, product_id)

这是预期的行为吗？在 on delete cascade 的情况下，删除父行中的行，在子行中删除 table，但同样的事情不会发生在 drop table ?

我错过了什么吗？这种行为是 postgres 特有的吗？

提前致谢。

Answer 1

(...) to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified. (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely.)

https://www.postgresql.org/docs/current/static/sql-droptable.html（强调我的）

Answer 2

因为 DROP ... CASCADE 就是这样设计的。

Quote from the manual

but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely

^{（强调我的）}

这不是 Postgres 特有的。删除表时，Oracle 和 DB2 的工作方式相同。

为什么 drop table cascade 没有删除 postgresql 中的 child table？

Why drop table cascade is not removing child table in postgresql?

postgresql

ddl

foreign-keys

drop-table