根據另一個表中列的值對列使用檢查約束

Question

我有一張桌子：

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

我還有一張桌子：

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 的值介於 1 和 member_count（含）之間。 我知道我需要在這里使用檢查約束，但我不知道如何使用另一個表的列。 我怎么做？

Answer 1

檢查約束不能引用其他表，因此您只需對INSERT和UPDATE使用 2 個單獨的觸發器即可實現您想要的：

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;

另外，我相信您應該更改表成員的定義，以便列team_id和member_number的組合是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)
);

見演示。