Oracle 11g Release 2

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CREATE TABLE PROJDEPT (
  proj_dept_id NUMBER CONSTRAINT projdept_pk PRIMARY KEY
);
CREATE TABLE PROJECT (
  project_id   NUMBER
               CONSTRAINT project_pk PRIMARY KEY,
  proj_dept_id NUMBER
               CONSTRAINT fk_project REFERENCES PROJDEPT ( proj_dept_id )
);
CREATE TABLE EMPLOYEE (
  Employee_ID  NUMBER
               CONSTRAINT employee_pk PRIMARY KEY,
  proj_dept_id NUMBER
               CONSTRAINT fk_EMPLOYEE REFERENCES PROJDEPT( proj_dept_id )
);
CREATE TABLE PROJECTTASK (
  ID           NUMBER
               CONSTRAINT projecttask_pk PRIMARY KEY,
  project_id   NUMBER
               CONSTRAINT fk_PROJECTTASK REFERENCES PROJECT( project_id ),
  employee_id  NUMBER
               CONSTRAINT fk_PROJECTTASK2 REFERENCES EMPLOYEE( employee_id )
);
ALTER TABLE PROJECTTASK DROP CONSTRAINT PROJECTTASK_pk
                        DROP CONSTRAINT fk_PROJECTTASK
                        DROP CONSTRAINT fk_PROJECTTASK2;
ALTER TABLE EMPLOYEE DROP CONSTRAINT EMPLOYEE_pk DROP CONSTRAINT fk_EMPLOYEE;
ALTER TABLE PROJECT DROP CONSTRAINT PROJECT_pk DROP CONSTRAINT fk_PROJECT;
ALTER TABLE PROJDEPT DROP CONSTRAINT PROJDEPT_pk;
ALTER TABLE PROJDEPT ADD CONSTRAINT PROJDEPT_pk PRIMARY KEY (Proj_Dept_ID);
ALTER TABLE EMPLOYEE ADD CONSTRAINT EMPLOYEE_pk PRIMARY KEY (Employee_ID);
ALTER TABLE EMPLOYEE 
  ADD CONSTRAINT fk_EMPLOYEE 
  FOREIGN KEY (Proj_Dept_ID)
  REFERENCES PROJDEPT(Proj_Dept_ID);
ALTER TABLE PROJECT ADD CONSTRAINT PROJECT_pk PRIMARY KEY (Project_ID);
ALTER TABLE PROJECT
  ADD CONSTRAINT fk_PROJECT 
  FOREIGN KEY (Proj_Dept_ID)
  REFERENCES PROJDEPT(Proj_Dept_ID);
ALTER TABLE PROJECTTASK ADD CONSTRAINT PROJECTTASK_pk PRIMARY KEY (Project_ID, Employee_ID);
ALTER TABLE PROJECTTASK 
  ADD CONSTRAINT fk_PROJECTTASK FOREIGN KEY (Project_ID) REFERENCES PROJECT(Project_ID);
ALTER TABLE PROJECTTASK 
  ADD CONSTRAINT fk_PROJECTTASK2 FOREIGN KEY (Employee_ID) REFERENCES EMPLOYEE(Employee_ID);