Question

Create table Course(CourseID char(5),CourseDesc varchar(25),CourseType char(9),SemNo int(1),FacID char(4) default 0);
alter table Course add primary key(CourseID);
alter table Course add foreign key(FacID) references Faculty1(FacID);

这里FacID是Faculty主键的外键当我插入值时，我尝试插入此值

insert into Course(CouseID,CourseDesc,CourseType,SemNo,FacID) values ('EE025','Digital Logic Circuits','Theory','4','');

但是，这会产生sql错误1452，请解决它。

Answer 1

您在插入中拼错了CourseID：

    data:any;
    questions : QuestionBase<any>[] = [];

    getQuestions() Observable<QuestionsBase[]> {
        return this.http.get(this.questionUrl)
            .map(res => res.json())
            .map(data => {
                this.data = data;
                this.buildQuestions(data);
    )};

    buildQuestions(data){
        for (let key in data) {
            //push Objects in this.questions array
        }
        return this.questions.sort((a, b) => a.order - b.order);
    }

应该是：

insert into Course(CouseID,CourseDes...

Answer 2

您是否确认Faculty1中有一行FacID = 0？

insert into Faculty1 (FacID /* other columns */) values (0 /*, other values*/ );
insert into Course(CourseID,CourseDesc,CourseType,SemNo,FacID) values ('EE025','Digital Logic Circuits','Theory',4,0);

如果要插入空值（''），则需要在Faculty1.FacID中包含空字符串值。否则，您可以正确指出'0'。

create table Faculty1(
    FacID char(4) not null primary key
);
insert into faculty1 values (0);

create table Course(
    CourseID char(5) not null
  , CourseDesc varchar(25)
  , CourseType char(9)
  , SemNo int
  , FacID char(4) not null default 0 
    /* specify not null to use default when value not inserted */
); 
alter table Course add primary key(CourseID);
alter table Course add foreign key(FacID) references Faculty1(FacID);

/* inserting `''` instead of `0` for FacId results in an error */
begin try;
insert into Course(CourseID,CourseDesc,CourseType,SemNo,FacID) values 
('EE025','Digital Logic Circuits','Theory','4','');
end try
begin catch
select error_message();
end catch;

/* inserting `0` for FacId = no error*/
insert into Course(CourseID,CourseDesc,CourseType,SemNo,FacID) values 
  ('EE025','Digital Logic Circuits','Theory',4,'0');
select * from Course;

/* inserting without specifying FacId uses default*/
insert into Course(CourseID,CourseDesc,CourseType,SemNo) values 
  ('EE026','Digital Logic Circuits','Theory',4);
select * from Course;

rextester演示：http://rextester.com/ZYGWRX20984

SQL错误1452：无法添加或更新子级

2 个答案: