Mysql 中“ON-DELETE-CASCADE”和“ON-DELETE-RESTRICT”约束混合的标准行为

Question

在mysql 5.6中，考虑这 2 个在 A、B、C 和 D 之间创建关系的示例。

实施例1

CREATE TABLE `a` (
    id INT UNSIGNED NOT NULL,
    PRIMARY KEY (id)
) ENGINE = INNODB;

CREATE TABLE `b` (
    id INT UNSIGNED NOT NULL,
    a INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (a) REFERENCES a (id) ON DELETE CASCADE
) ENGINE = INNODB;

CREATE TABLE `c` (
    id INT UNSIGNED NOT NULL,
    a INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (a) REFERENCES a (id) ON DELETE CASCADE
) ENGINE = INNODB;

CREATE TABLE `d` (
    id INT UNSIGNED NOT NULL,
    b INT UNSIGNED NOT NULL,
    c INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (id) REFERENCES b (id) ON DELETE CASCADE,
    FOREIGN KEY (id) REFERENCES c (id) ON DELETE RESTRICT
) ENGINE = INNODB;

INSERT INTO a VALUES (1);
INSERT INTO b VALUES (1, 1);
INSERT INTO c VALUES (1, 1);
INSERT INTO d VALUES (1, 1, 1);

DELETE FROM a;

结果是所有行都被删除。

实施例2

CREATE TABLE `a` (
    id INT UNSIGNED NOT NULL,
    PRIMARY KEY (id)
) ENGINE = INNODB;

CREATE TABLE `b` (
    id INT UNSIGNED NOT NULL,
    a INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (a) REFERENCES a (id) ON DELETE CASCADE
) ENGINE = INNODB;

CREATE TABLE `c` (
    id INT UNSIGNED NOT NULL,
    a INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (a) REFERENCES a (id) ON DELETE CASCADE
) ENGINE = INNODB;

CREATE TABLE `d` (
    id INT UNSIGNED NOT NULL,
    b INT UNSIGNED NOT NULL,
    c INT UNSIGNED NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (id) REFERENCES b (id) ON DELETE RESTRICT,
    FOREIGN KEY (id) REFERENCES c (id) ON DELETE CASCADE
) ENGINE = INNODB;

INSERT INTO a VALUES (1);
INSERT INTO b VALUES (1, 1);
INSERT INTO c VALUES (1, 1);
INSERT INTO d VALUES (1, 1, 1);

DELETE FROM a;

请注意，唯一的区别是d中的RESTRICT外键发生了变化。然而，这个例子失败了

错误代码：1451 无法删除或更新父行：外键约束失败 ( hello. d, CONSTRAINT d_ibfk_1FOREIGN KEY ( id) REFERENCES b( id))

从逻辑上讲，它与示例 1相同。在没有查看MySQL的源代码的情况下，我强烈怀疑外键是根据其名称按词汇顺序“应用”的。在这种情况下，标准行为 (ANSI-SQL) 是什么？

Answer 1

我修改了示例 1，以便我尝试过的所有供应商都接受该语法。事实证明，测试中唯一拒绝该场景的 DBMS 是 Db2 DB<>Fiddle：

MariaDB 10.2, 10.3 Yes
MySQL 5.6, 5.7, 8.0 Yes
Postgres 11 Yes

Oracle 11g release 2, 18 Yes
SQLServer 2017 Yes
Db2 V11 No

请注意，对于 Oracle 和 SQLServer，必须稍微修改外键。查看迪内什·库马尔提供的链接

Oracle SQL服务器

Db2 抛出如下异常：

SQL20255N FOREIGN KEY .. 无效，因为它将导致后代表...通过具有冲突的删除规则的多个关系删除连接到其祖先表。冲突发生在后代表上的约束... 和... 的删除规则之间。原因代码=“3”。SQLSTATE=42915 SQLCODE=-20255

我浏览了 7IWD2-02-Foundation-2011-12.pdf，可以从以下位置下载：

http://www.wiscorp.com/sql20nn.zip

但我没有找到任何与此相关的内容。

对我来说，Db2 在这方面似乎表现得很理智，但这只是我的看法。