Question

这里我在从teacher_detils表初始化外键时遇到错误。这里我使用sql-server for database

错误是 - 引用的表'teacher_details'中没有主键或候选键与外键'fk_exam_details'中的引用列列表匹配。 Msg 1750，Level 16，State 0，Line 43 无法创建约束或索引。查看以前的错误。

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Answer 1

该错误是因为您尝试在外键中引用非PK列teacher_user_id，因为，teacher_details具有两列的复合键--id和email。

如果teacher_user_id可以有多个email_id，那么我建议您在teacher_details表中使用教师ID PK。

create table teacher_details(
    teacher_user_id varchar(30) not null,
    teacher_name varchar(60) not null
)

/*Alter teacher_details table for primary key*/


alter table teacher_details
add constraint pk_teacher_details primary key (teacher_user_id)

并创建一个单独的表来保存teacher_user_id的电子邮件：

create table teacher_emails(
    id int identity(1,1) primary key,
    teacher_user_id varchar(30) not null,
    teacher_email varchar(50) not null
)

alter table teacher_emails
add constraint fk_teacher_emails 
    FOREIGN KEY (teacher_user_id) REFERENCES teacher_details(teacher_user_id)

现在你可以按照你想要的方式创建这个FK：

/* Table for exam */

create table exam_details(
    exam_id varchar(30) not null,
    teacher_user_id varchar(30) not null,
)

/* edited the drop table command to avoid confusion*/

/*Alter exam_details for primary key*/

alter table exam_details
add constraint fk_exam_details FOREIGN KEY (teacher_user_id)
    REFERENCES teacher_details(teacher_user_id)

如果不是这种情况，即每个user_id只能有一个唯一的电子邮件，那么就不需要额外的电子邮件表。只需使用：

create table teacher_details(
    teacher_user_id varchar(30) not null,
    teacher_name varchar(60) not null,
    teacher_email varchar(50) unique not null
)

alter table teacher_details
add constraint pk_teacher_details primary key (teacher_user_id)

为什么在初始化外键时出错？

1 个答案: