錯誤：沒有唯一的約束匹配給定的鍵

Question

由於某種原因，我得到一個錯誤*在我的代碼。我對PostgresSQL很陌生，只是SQL。什麼導致了這個錯誤？

*沒有與參考表「tech」的給定鍵匹配的唯一約束。

BEGIN; 

CREATE TABLE Person (
    person_id SERIAL PRIMARY KEY, 
    firstname VARCHAR(128), 
    lastname VARCHAR(128), 
    email_adr VARCHAR(128), 

    UNIQUE(person_id, email_adr) 
); 

CREATE TABLE Phone (
    person_id INT REFERENCES Person(person_id), 
    phone_nr INT PRIMARY KEY, 

    UNIQUE(phone_nr) 
); 


CREATE TABLE Tech (
    tech_id INT REFERENCES Person(person_id), 
    username VARCHAR(80) PRIMARY KEY, 
    password VARCHAR(80) NOT NULL, 
    location Varchar(128), 

    UNIQUE(username, tech_id) 
); 

CREATE TABLE Customer (
    customer_id INT REFERENCES Persons(person_id), 
    addresse  VARCHAR(255) NOT NULL, 

    UNIQUE(customer_id) 
); 

CREATE TABLE Task (
    task_id  SERIAL PRIMARY KEY, 
    payment  MONEY, 
    tech  INT REFERENCES Tech(tech_id)   NOT NULL, 
    customer INT REFERENCES Customer(customer_id) NOT NULL, 
    start_date DATE         NOT NULL, 
    end_dato DATE, 

    UNIQUE(tech, customer, start_date, end_date) 
); 

COMMIT; 

Answer 1

在表Task你試圖通過tech_id引用表Tech。爲此，您必須在Tech中添加UNIQUE CONSTRAINT至tech_id。 現在在表Tech你有UNIQUE(username, tech_id)，這意味着tech_id列的值可能會增加一倍。

Tech 
------------------------------- 
tech_id  username, .... 
------------------------------ 
1   'John' 
2   'Tony' 
1   'Nataly' 

Acctually的更好的主意是PRIMARY KEY設定基準，所以你的情況username表Tech。

如果您想要保留結構中存在問題的方式，您應該在Tech列中添加UNIQUE(tech_id)。

Answer 2

您對這段代碼有什麼看法？

BEGIN; 

CREATE TABLE Person (
    person_id SERIAL PRIMARY KEY, 
    firstname VARCHAR(128), 
    lastname VARCHAR(128), 
    email_adr VARCHAR(128), 

    UNIQUE(person_id), 
    UNIQUE(email_adr) 
); 

CREATE TABLE Phone (
    person_id INT, 
    phone_nr INT PRIMARY KEY, 
); 


CREATE TABLE Tech (
    tech_id INT, 
    username VARCHAR(80) PRIMARY KEY, 
    password VARCHAR(80) NOT NULL, 
    location Varchar(128), 

    FOREIGN KEY(tech_id) REFERENCES Person(person_id), 
    UNIQUE(username), 
    UNIQUE(tech_id) 
); 

CREATE TABLE Customer (
    customer_id INT REFERENCES Persons(person_id), 
    addresse  VARCHAR(255) NOT NULL, 

    FOREIGN KEY(tech_id) REFERENCES Person(person_id), 
    UNIQUE(customer_id) 
); 

CREATE TABLE Task (
    task_id  SERIAL PRIMARY KEY, 
    payment  MONEY, 
    tech  varchar(80) REFERENCES Tech(username)  NOT NULL, 
    customer INT  REFERENCES Customer(customer_id) NOT NULL, 
    start_date DATE         NOT NULL, 
    end_dato DATE, 

    UNIQUE(tech, customer, start_date, end_date) 
); 

COMMIT;