错误的外键语法和错误的引用表名（如果表名为department，则不能引用dept_rudra）。

SQL> CREATE TABLE department
  2  (
  3     deptid   INT PRIMARY KEY,
  4     dname    VARCHAR (255)
  5  );

Table created.

您可以使用各种选项（inline、out-of-line、using alter table）-无论您选择什么，只要语法正确，都可以工作。

SQL> CREATE TABLE employee
  2  (
  3     eid      INT PRIMARY KEY,
  4     ename    VARCHAR (255),
  5     deptid   INT CONSTRAINT fk_ed REFERENCES department (deptid)
  6  );

Table created.

或

SQL> DROP TABLE employee;

Table dropped.

SQL> CREATE TABLE employee
  2  (
  3     eid      INT PRIMARY KEY,
  4     ename    VARCHAR (255),
  5     deptid   INT,
  6     --
  7     CONSTRAINT fk_ed FOREIGN KEY (deptid) REFERENCES department (deptid)
  8  );

Table created.

或

SQL> DROP TABLE employee;

Table dropped.

SQL> CREATE TABLE employee
  2  (
  3     eid      INT PRIMARY KEY,
  4     ename    VARCHAR (255),
  5     deptid   INT,
  6     --
  7     FOREIGN KEY (deptid) REFERENCES department (deptid)
  8  );

Table created.

或

SQL> DROP TABLE employee;

Table dropped.

SQL> CREATE TABLE employee
  2  (
  3     eid      INT PRIMARY KEY,
  4     ename    VARCHAR (255),
  5     deptid   INT
  6  );

Table created.

SQL> ALTER TABLE employee ADD CONSTRAINT fk_ed FOREIGN KEY (deptid)
  2    REFERENCES department (deptid);

Table altered.

SQL>

create table employee(
eid int primary key,
ename varchar(255),
deptid int,
foreign key (deptid) references department(deptid)
);