使用主键和 2 个外键创建表

Question

创建 WPC 分配表。 注意：有一个复合主键和 2 个外键，需要 3 个约束。 见下图 2-44 取自教科书。 另外，请记住，同一架构中的两个约束不能具有相同的名称。 以下是部分 DDL 供您完成：

CREATE TABLE ASSIGNMENT 
(
    EmployeeNumber INTEGER NOT NULL, 
    ProjectID INTEGER NOT NULL,
    Hoursworked NUMBER (6,2),

    CONSTRAINT PK_Assignment 
        PRIMARY KEY (EmployeeNumber, ProjectID),

    CONSTRAINT FK_Assignment_EMPLOYEE 
        FOREIGN KEY (EmployeeNumber) REFERENCES EMPLOYEE,…

（请自行填写本声明的其余部分）

我收到一个错误：

从第 1 行开始的错误命令：

CREATE TABLE ASSIGNMENT 
(
    EmployeeNumber INTEGER NOT NULL,
    ProjectID INTEGER NOT NULL,
    Hoursworked NUMBER (6,2),

    CONSTRAINT PK_Assignment 
        PRIMARY KEY (EmployeeNumber, ProjectID),
    CONSTRAINT FK_Assignment_EMPLOYEE 
        FOREIGN KEY (EmployeeNumber), 
    CONSTRAINT FK_Project_Assignment 
        FOREIGN KEY (ProjectID) REFERENCES EMPLOYEE.employeenumber(EmployeeNumber), PROJECT.projectID(ProjectId)
)

错误报告：

ORA-00905: 缺少关键字
00905. 00000 - “缺少关键字”
*原因：
*行动：

我找不到我缺少的东西..有人可以帮忙吗？

Answer 1

您选择创建轮廓约束（这完全可以，只要您遵循语法）。 仅提及另一个选项，也许您会发现它们很有用。

请注意，不必将构成主键的列明确声明为not null因为主键约束无论如何都不会接受空值。

---

大纲约束（它们遵循列的定义）：

SQL> create table assignment
  2  (   employeenumber integer,
  3      projectid      integer,
  4      hoursworked    number (6,2),
  5      constraint pk_assignment
  6          primary key (employeenumber, projectid),
  7      constraint fk_assignment_employee
  8          foreign key (employeenumber) references employee (employeenumber),
  9      constraint fk_project_assignment
 10          foreign key (projectid) references project (projectid)
 11  );

Table created.

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内联约束，与列在同一行； 由于有一个复合主键（由两列或多列组成），它不能是内联的：

SQL> create table assignment
  2  (   employeenumber integer constraint fk_assignment_employee
  3                             references employee (employeenumber),
  4      projectid      integer constraint fk_project_assignment
  5                             references project (projectid),
  6      hoursworked    number (6,2),
  7      constraint pk_assignment
  8          primary key (employeenumber, projectid)
  9  );

Table created.

---

表是单独创建的，约束是使用ALTER TABLE命令创建的：

SQL> create table assignment
  2  (   employeenumber integer,
  3      projectid      integer,
  4      hoursworked    number (6,2)
  5  );

Table created.

SQL> alter table assignment add constraint pk_assingment primary key (employeenumber, projectid);

Table altered.

SQL> alter table assignment add constraint fk_assignment_employee
  2    foreign key (employeenumber) references employee (employeenumber);

Table altered.

SQL> alter table assignment add constraint fk_project_assignment
  2    foreign key (projectid) references project (projectid);

Table altered.