Question

我使用postgresql，并创建一些表。有用户＆＃39;表

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

..还有一张书桌

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

我尝试制作关系表

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
);

如何做得更好，不显示消息：

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

？谢谢！

Answer 1

外键无法引用非唯一字段，因为它需要引用唯一行。

您需要将引用的字段设为PRIMARY KEY;

CREATE TABLE users (
  id serial NOT NULL PRIMARY KEY,

...或者只是将它UNIQUE;

CREATE TABLE books (
  id serial NOT NULL UNIQUE,

An SQLfiddle showing both versions working to create the tables

Postgresql和关系表

1 个答案: