-- 
-- Consider the Following SQL Schema definition code
-- that does not enforce any rules.
-- Your job is to write the sql statements to enforce the business rules
-- attached to the end of this schema definition code
-- 
-- Make sure that your code is syntactically Correct.
-- General Guidlines
-- All primary keys, foreign keys and check constraints are out side the table definition
-- Useing Alter table
-- 
CREATE TABLE xemployee( 
	fname 		varchar(15), 
      	minit 		char,
     	lname 		varchar(15),
      	ssn 		char(9),
      	bdate 		date, 
      	address 	varchar(30),
      	sex 		char,
      	salary 		decimal(10,2),
      	superssn 	char(9),
      	dno 		number);

CREATE TABLE xdepartment( 
	dname 		varchar(15),
      	dnumber 	number,
      	mgrssn 		char(9), 
      	mgrstartdate 	date);

CREATE TABLE xdept_locations( 
     	dnumber 	number,
      	dlocation 	varchar(15));

CREATE TABLE xproject( 
     	pname 		varchar(15),
      	pnumber		number,
      	plocation 	varchar(15),
      	dnum 		number);

CREATE TABLE xworks_on( 
     	essn 		char(9),
      	pno 		number,
      	hours 		DECIMAL(3,1));

CREATE TABLE xdependent( 
     	essn 		char (9),
      	dependent_name 	varchar(15),
      	sex 		char,
      	bdate 		date,
      	relationship 	varchar(8));
-------
------- Write the necessary SQL constraints to enforce the following Business Rules
------- 
-- Employee Table Constraints: 
---- fname is required
---- lname is required
---- bdate defaults to system date
---- dno is required
---- primary key(ssn)
---- Foreign key(superssn) 	references employee(ssn)
---- Foreign key(dno)	references department(dnumber)

-- department Table Constraints:
---- dname is required
---- dnumber is required
---- mgrssn is required
---- mgrstartdate defaults to system date
---- dname is a candidate key
---- primary key(dnumber)
---- foreign key(mgrssn) references employee(ssn)

-- dept_locations Table Constraints: 
---- dnumber is required
---- dlocation is required
---- primary key(dnumber, dlocation)
---- Foreign key(dnumber) references department(dnumber)

-- project Table Constraints: 
---- pname is required
---- pnumber is required
---- dnum is required
---- pname is a candidate key
---- primary key(pnumber)
---- foreign key(dnum) references department(dnumber)

---- works_on Table Constraints: 
---- essn is required
---- pno is required
---- hours is required
---- PRIMARY KEY(ESSN, PNO)
---- FOREIGN KEY(essn) references employee(ssn)
---- foreign key(pno) references project(pnumber)

-- dependent Table Constraints: 
----  essn is unique
----  dependent_name is unique
----  primary key(essn, dependent_name)
----  foreign key(essn) references employee(ssn)