Postgresql和關係表

Question

我使用postgresql，並創建一些表。 有用戶表

CREATE TABLE myschem.users (
    id serial NOT NULL, name character varying(255),email character varying(255) 
) WITH (OIDS=FALSE); 

..和有一個books表

CREATE TABLE myschem.books (
    id serial NOT NULL, title character varying(255),author character varying(255) 
) WITH (OIDS=FALSE); 

，我嘗試做一個關係表

CREATE TABLE myschem.bookloans 
(
    uid integer, -- user id 
    bid integer, -- book id 
    primary key (uid, bid), 
    FOREIGN KEY (uid) REFERENCES myschem.users (id) ON DELETE CASCADE ON UPDATE CASCADE, 
    FOREIGN KEY (bid) REFERENCES myschem.rooms (id) ON DELETE CASCADE ON UPDATE CASCADE 
); 

如何做的更好，它確實不顯示消息：

ERROR: there is no unique constraint matching given keys for referenced table "users" 

？ 謝謝！

Answer 1

外鍵無法引用非唯一字段，因爲它需要引用唯一的行。

您需要將參考字段設置爲PRIMARY KEY;

CREATE TABLE users (
    id serial NOT NULL PRIMARY KEY, 

...或只是讓它UNIQUE;

CREATE TABLE books (
    id serial NOT NULL UNIQUE, 

An SQLfiddle showing both versions working to create the tables。