SQL：使用复合引用主键和外键创建表

所以我有下面的ER图：

因此，微妙是一种概括。这些东西要么是金属做的，要么是木头做的，它不可能只是一个小玩意儿。以下是创建代码：

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)
);

我想让Metal同时拥有一个主键（SubthingID，由组成）和一个外键（requires，引用DustID）。我不能在事后将其声明为外键，因为（SubthingID，composes_of）已经是外键。

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你怎么能解决这个问题，除了把需求做成表格？

没关系，我太蠢了

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)
);

很好用