关系模式和完整性约束

Question

请问是否可以使用创建脚本在此架构上创建这些完整性约束？

1. 俱乐部 (klub) 只能有一名教练 (trener)
2. 俱乐部只能有一位所有者 (majitel)
3. 每个成员 (člen) 只能加入一个俱乐部
4. 教练只能为他的俱乐部设置战术 (taktika)？

是否可以通过创建脚本中的完整性约束来解决这个问题，或者是否使用触发器来解决这个问题？我是我的创建脚本的一部分。

架构

创建脚本

CREATE TABLE club (
id_club SERIAL NOT NULL,
nazev VARCHAR(256) NOT NULL,
datum_zalozeni VARCHAR(256) NOT NULL
);
ALTER TABLE club ADD CONSTRAINT pk_club PRIMARY KEY (id_club);
ALTER TABLE club ADD CONSTRAINT uc_club_nazev UNIQUE (nazev);

CREATE TABLE coach (
    id_member INTEGER NOT NULL
);
ALTER TABLE coach ADD CONSTRAINT pk_coach PRIMARY KEY (id_member);

CREATE TABLE member (
    id_member SERIAL NOT NULL,
    id_club INTEGER NOT NULL,
    jmeno VARCHAR(256) NOT NULL,
    prijmeni VARCHAR(256) NOT NULL,
    narodnost VARCHAR(256) NOT NULL,
    datum_narozeni VARCHAR(256) NOT NULL
);
ALTER TABLE member ADD CONSTRAINT pk_member PRIMARY KEY (id_member);

CREATE TABLE owner (
    id_member INTEGER NOT NULL
);
ALTER TABLE owner ADD CONSTRAINT pk_owner PRIMARY KEY (id_member);

CREATE TABLE player (
    id_member INTEGER NOT NULL,
    cislo VARCHAR(256) NOT NULL,
    post VARCHAR(256) NOT NULL
);
ALTER TABLE player ADD CONSTRAINT pk_player PRIMARY KEY (id_member);

ALTER TABLE coach ADD CONSTRAINT fk_coach_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;

ALTER TABLE member ADD CONSTRAINT fk_member_club FOREIGN KEY (id_club) REFERENCES club (id_club) ON DELETE CASCADE;

ALTER TABLE owner ADD CONSTRAINT fk_owner_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;

ALTER TABLE player ADD CONSTRAINT fk_player_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;
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Answer 1

无法对当前架构强制实施所需的约束。您需要的是唯一约束，但唯一约束适用于单表数据，并且您没有包含成员角色和俱乐部信息的表。

为了实现它们，您必须将带有角色信息的新列添加到 clen 表（成员），或将俱乐部信息添加到 trener 和 majitel 表。因为一个成员可以有多个角色，所以第一个解决方案不是一个选项。

仅添加一个俱乐部可能会导致数据一致性问题（有人更改了会员的俱乐部 ID，但没有更改教练的 ID）。为了保证完整性，我在一对（member_id、club_id）上添加了外键。

结果是：

CREATE TABLE club (
id_club SERIAL NOT NULL,
nazev VARCHAR(256) NOT NULL,
datum_zalozeni VARCHAR(256) NOT NULL
);
ALTER TABLE club ADD CONSTRAINT pk_club PRIMARY KEY (id_club);
ALTER TABLE club ADD CONSTRAINT uc_club_nazev UNIQUE (nazev);

CREATE TABLE coach (
    id_member INTEGER NOT NULL
);
ALTER TABLE coach ADD CONSTRAINT pk_coach PRIMARY KEY (id_member);

CREATE TABLE member (
    id_member SERIAL NOT NULL,
    id_club INTEGER NOT NULL,
    jmeno VARCHAR(256) NOT NULL,
    prijmeni VARCHAR(256) NOT NULL,
    narodnost VARCHAR(256) NOT NULL,
    datum_narozeni VARCHAR(256) NOT NULL
);
ALTER TABLE member ADD CONSTRAINT pk_member PRIMARY KEY (id_member);

CREATE TABLE owner (
    id_member INTEGER NOT NULL
);
ALTER TABLE owner ADD CONSTRAINT pk_owner PRIMARY KEY (id_member);

CREATE TABLE player (
    id_member INTEGER NOT NULL,
    cislo VARCHAR(256) NOT NULL,
    post VARCHAR(256) NOT NULL
);
ALTER TABLE player ADD CONSTRAINT pk_player PRIMARY KEY (id_member);

ALTER TABLE coach ADD CONSTRAINT fk_coach_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;

ALTER TABLE member ADD CONSTRAINT fk_member_club FOREIGN KEY (id_club) REFERENCES club (id_club) ON DELETE CASCADE;

ALTER TABLE owner ADD CONSTRAINT fk_owner_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;

ALTER TABLE player ADD CONSTRAINT fk_player_member FOREIGN KEY (id_member) REFERENCES member (id_member) ON DELETE CASCADE;

--We need a unique constraint on (id_member, id_club), to be able to use the pair in a foreign key.
ALTER TABLE member ADD CONSTRAINT unq_member_and_club UNIQUE(id_member, id_club);

--Req. 1: club (klub) can have exactly one coach (trener)
ALTER TABLE coach ADD COLUMN id_club integer;
ALTER TABLE coach ADD CONSTRAINT fk_coach_club FOREIGN KEY (id_club) REFERENCES club (id_club);
ALTER TABLE coach ADD CONSTRAINT fk_coach_member_and_club FOREIGN KEY (id_member, id_club) REFERENCES member (id_member, id_club);
ALTER TABLE coach ADD CONSTRAINT fk_single_coach_per_club UNIQUE(id_club);

--Req. 2: club can have just one owner (majitel)
ALTER TABLE owner ADD COLUMN id_club integer;
ALTER TABLE owner ADD CONSTRAINT fk_owner_club FOREIGN KEY (id_club) REFERENCES club (id_club);
ALTER TABLE owner ADD CONSTRAINT fk_owner_member_and_club FOREIGN KEY (id_member, id_club) REFERENCES member (id_member, id_club);
ALTER TABLE owner ADD CONSTRAINT fk_single_owner_per_club UNIQUE(id_club);

您可以在db<>fiddle中测试脚本。

请注意，我添加了fk_coach_club 和fk_owner_club 外键约束，尽管它们不是强制性的。 fk_member_club、fk_owner_member_and_club 和 fk_coach_member_and_club 一起确保 club_id 值在 owner 和 coach 表中始终有效，但如果我觉得拥有这些 FK 是自然的。

要求。 3 每个成员 (člen) 只能在一个俱乐部中 在您的架构中无需更改任何内容，成员具有俱乐部属性，无法将另一个俱乐部分配给单个成员。

对于Req.4没有特殊限制，教练只能为他的俱乐部设置战术（taktika），因为战术是由分配给单个俱乐部的教练设置的，所以没有需要约束。