sql - 根据另一个表中列的值对列使用检查约束

Question

我有一张 table :

CREATE TABLE teams (
    id INTEGER PRIMARY KEY,
    member_count INTEGER NOT NULL
);

我还有另一张 table :

CREATE TABLE members (
    id INTEGER PRIMARY KEY,
    team_id INTEGER,
    member_number INTEGER
    FOREIGN KEY (team_id) REFERENCES teams (id)
);

我希望member_number 的值介于1 和member_count(含)之间。我知道我需要在这里使用检查约束，但我不知道如何使用另一个表的列来做到这一点。我该怎么做？

Answer 1

检查约束不能引用其他表，因此您只需使用 INSERT 和 UPDATE 两个单独的触发器即可实现您想要的效果:

CREATE TRIGGER insert_member_number BEFORE INSERT ON members
BEGIN
  SELECT
    CASE
      WHEN NEW.member_number NOT BETWEEN 1 AND (SELECT member_count FROM teams WHERE id = NEW.team_id) 
        THEN RAISE (ABORT, 'Invalid member number')
    END;
END;

CREATE TRIGGER update_member_number BEFORE UPDATE ON members
BEGIN
  SELECT
    CASE
      WHEN NEW.member_number NOT BETWEEN 1 AND (SELECT member_count FROM teams WHERE id = NEW.team_id) 
        THEN RAISE (ABORT, 'Invalid member number')
    END;
END;

此外，我认为您应该更改表成员的定义，以便列 team_id 和 member_number 的组合是 UNIQUE:

CREATE TABLE members (
    id INTEGER PRIMARY KEY,
    team_id INTEGER NOT NULL,
    member_number INTEGER NOT NULL,
    UNIQUE(team_id, member_number),
    FOREIGN KEY (team_id) REFERENCES teams (id)
);

请参阅demo .