SQL：使用复合引用主键和外键创建表

Question

所以我有以下ER图：

所以Subthing是一种概括。东西要么是用金属制成的，要么用木材制成，它不能只是一个副东西。这是创建代码：

CREATE TABLE Thing (
    ThingID INTEGER PRIMARY KEY NOT NULL
);

CREATE TABLE Subthing (
    consists_of INTEGER REFERENCES Thing(ThingID),
    SubthingID INTEGER NOT NULL,
    PRIMARY KEY (SubthingID, consists_of)
);

CREATE TABLE Wood (
    Wstuff VARCHAR(40) NOT NULL,
    consists_of INTEGER NOT NULL,
    SubthingID INTEGER NOT NULL,
    FOREIGN KEY (SubthingID, consists_of) REFERENCES Subthing(SubthingID, consists_of),
    PRIMARY KEY (SubthingID, consists_of)
);

CREATE TABLE Dust (
    DustID INTEGER PRIMARY KEY NOT NULL
);

CREATE TABLE Metal (
    Mstuff VARCHAR(40) NOT NULL,
    consists_of INTEGER NOT NULL,
    SubthingID INTEGER NOT NULL,
    requires INTEGER NOT NULL REFERENCES Dust(DustID),
    FOREIGN KEY (SubthingID, consists_of) REFERENCES Subthing(SubthingID, consists_of),
    PRIMARY KEY (SubthingID, consists_of)
);

我想要的是Metal同时拥有一个引用（SubthingID，composed_of）的主键和一个带有requires的外键，引用DustID。事实之后，我无法将其声明为外键，因为（SubthingID，composed_of）已经是外键。 你怎么能解决这个问题，除了把要求变成一张桌子？

Answer 1

没关系，我太傻了。

CREATE TABLE Metal (
    Mstuff VARCHAR(40) NOT NULL,
    consists_of INTEGER NOT NULL,
    SubthingID INTEGER NOT NULL,
    requires INTEGER NOT NULL,
    FOREIGN KEY (requires) REFERENCES Dust(DustID),
    FOREIGN KEY (SubthingID, consists_of) REFERENCES Subthing(SubthingID,     consists_of),
    PRIMARY KEY (SubthingID, consists_of)
);

工作得很好。