SQL错误：ORA-00922：创建复合键的选项丢失或无效

Question

我正在尝试使用emp_id和licence_cert_no为我的表创建一个复合主键，为什么这不起作用？

CREATE TABLE employee_licence_certificate(emp_id NUMBER(4) REFERENCES employee(emp_id)
, licence_cert_code VARCHAR2(6) REFERENCES licence_certificate(licence_cert_code)
, date_earned DATE NOT NULL) 
CONSTRAINT pk_emp_licence PRIMARY KEY(emp_id, licence_cert_code)

错误消息：

Error starting at line 1 in command:
CREATE TABLE employee_licence_certificate(emp_id NUMBER(4) REFERENCES employee(emp_id)
, licence_cert_code VARCHAR2(6) REFERENCES licence_certificate(licence_cert_code)
, date_earned DATE NOT NULL) 
CONSTRAINT pk_emp_licence PRIMARY KEY(emp_id, licence_cert_code)
Error at Command Line:3 Column:29
Error report:
SQL Error: ORA-00922: missing or invalid option
00922. 00000 -  "missing or invalid option"
*Cause:    
*Action:

Answer 1

CONSTRAINT子句需要放在括号内：

CREATE TABLE employee_licence_certificate(
  emp_id NUMBER(4) REFERENCES employee(emp_id)
, licence_cert_code VARCHAR2(6) REFERENCES licence_certificate(licence_cert_code)
, date_earned DATE NOT NULL
, CONSTRAINT pk_emp_licence PRIMARY KEY(emp_id, licence_cert_code)
);

（reference）