1. Constraints CSED421 Database Systems Lab

2. Constraints To define an integrity constraint (IC) –IC : condition that must be true for any instance of the database 5 types of constraints –NOT NULL constraints –UNIQUE constraints –PRIMARY KEY constraints –FOREIGN KEY constraints –CHECK constraints

3. Specification As part of the table definition e.g., CREATE TABLE orders ( order_id NUMBER PRIMARY KEY, price NUMBER NOT NULL, … ); CREATE TABLE ( [ CONSTRAINT ], … );

4. Specification (cont.) Alteration after the table definition e.g., ALTER TABLE orders ADD PRIMARY KEY (order_id); e.g., ALTER TABLE orders MODIFY ( price NOT NULL ); ALTER TABLE ADD[DROP] [ CONSTRAINT ] ; ALTER TABLE MODIFY ( [ CONSTRAINT ] );

5. NOT NULL Constraint Prohibits a database value from being null –null : either unknown or not applicable To satisfy a NOT NULL constraint, every row in the table must contain a value for the column CREATE TABLE student ( sid NUMBER NOT NULL, … … … ); ALTER TALBE student MODIFY sid NOT NULL;

6. UNIQUE Constraint Prohibits multiple rows from having the same value in the same column or combination of columns. But allows some values to be null. CREATE TABLE promotions ( promo_id NUMBER UNIQUE, … … … ); ALTER TABLE promotions ADD UNIQUE (promo_id); ALTER TABLE promotions MODIFY promo_id UNIQUE;

7. PRIMARY KEY Constraint Prohibits multiple rows from having the same value in the same column or combination of columns and prohibits values from being null. Combines a NOT NULL constraint and a unique constraint in a single declaration. CREATE TABLE locations ( location_id NUMBER PRIMARY KEY, … … … ); ALTER TABLE locations ADD PRIMARY KEY (location_id); ALTER TABLE locations MODIFY location_id PRIMARY KEY;

8. PRIMARY KEY Constraint (cont.) CREATE TABLE locations ( nameCHAR(20), addrCHAR(20), … …, CONSTRAINT name_addr PRIMARY KEY (name, addr) ); ALTER TABLE locations ADD CONSTRAINT name_addr PRIMARY KEY (name, addr)

9. FOREIGN KEY Constraint Requires values in one table to match values in another table. Also called referential integrity constraint CREATE TABLE enrolled ( sid CHAR(20), … … …, CONSTRAINT fk_enrolled FOREIGN KEY (sid) REFERENCES students(sid) ); CREATE TABLE enrolled ( sid CHAR(20) REFERENCES students(sid) … … … ); ALTER TABLE enrolled ADD CONSTRAINT fk_enrolled FOREIGN KEY (sid) REFERENCES students(sid); ALTER TABLE enrolled MODIFY sid REFERENCES students(sid);

10. FOREIGN KEY Constraint What if a student tuple is deleted… –NO ACTION (default) –CASCADE / SET NULL CREATE TABLE Enrolled( … … …, FOREIGN KEY (sid) REFERENCES Students(sid) ON DELETE CASCADE / SET NULL ); sidcidgrade 53666Carnatic101C 53666Reggae203B 53650Topology112A 53666'History105B sidnameloginagegpa 53666Jonesjones@cs183.4 53688Smithsmith@eecs183.2 53650Smithsmith@math193.8 EnrolledStudents

11. CHECK Constraint Requires a value in the database to comply with a specified condition CREATE TABLE emp ( … … …, age NUMBER CHECK (age > 0) ); ALTER TABLE emp ADD CHECK (age > 0); ALTER TABLE emp MODIFY age CHECK (age > 0);

12. Practice 1 1.Bank_Acct 와 Customer_Info 테이블을 생성 Customer_Info : name VARCHAR2(20), addr VARCHAR(60), phone CHAR(10), email VARCHAR2(40) Bank_Acct : acct CHAR(4), name VARCHAR2(20), addr VARCHAR2(60), balance REAL Customer_Info’s primary key is (name, addr) Bank_Acct’s primary key is acct Bank_Acct’s (name, addr) references Customer_Info’s (name, addr)

13. Practice 1 2. 두 테이블에 대한 위의 인스턴스에 대해 오류 (IC) 를 찾기 3. 두 테이블에 각각의 레코드를 IC 를 만족하도록 필드 값을 수정하여 추가하기 NameAddrPhoneEmail Jones11 First St603-222-3456Jones@cs Smith12 First St603-333-5567Smith@cs Green14 Fourth St781-444-7890Green@cs Gates11 First St122-333-6789Gates@ms Smith12 Second St603-978-8765Smith@ee AcctNameAddrbalance 1005Jones11 First St1023 1002Smith12 First St22 1003Smith12 First St1100 1008Green14 Fourth St1077 1010Gates20 Tenth St50000 1012Smith15 Second St443 Bank_AcctCustomer_Info

14. Practice 1 4. 아래의 SQL 을 수행결과를 확인 SELECT B.name, C.email FROM Bank_Acct B, Customer_Info C WHERE B.name = C.name AND B.addr = C.addr AND B.balance > 1000.00

15. Practice 2 Simulate violation of integrity constraint 1.@practice2 스크립트를 통해 테이블 생성. Practice2 스크립트는 Enrolled 와 Students 테이블 을 생성하고, Enrolled 의 Students 를 참조하는 foreign key constraint 를 추가한다. sidcidgrade 53666Carnatic101C 53666Reggae203B 53650Topology112A 53666'History105B sidnameloginagegpa 53666Jonesjones@cs183.4 53688Smithsmith@eecs183.2 53650Smithsmith@math193.8 EnrolledStudents

16. Practice 2 practice2.sql CREATE TABLE Students ( sid CHAR(20) PRIMARY KEY, name CHAR(20), login CHAR(10), age INTEGER, gpa REAL ); CREATE TABLE Enrolled ( sid CHAR(20), cid CHAR(20), grade CHAR(2), CONSTRAINT fk_enrolled FOREIGN KEY (sid) REFERENCES Students (sid) ); INSERT INTO Students VALUES ('53666', 'Jones', 'jones@cs', 18, 3.4); INSERT INTO Students VALUES ('53688', 'Smith', 'smith@eecs', 18, 3.2); INSERT INTO Students VALUES ('53650', 'Smith', 'smith@math', 19, 3.8); INSERT INTO Enrolled VALUES ('53666', 'Carnatic101', 'C'); INSERT INTO Enrolled VALUES ('53666', 'Reggae203', 'B'); INSERT INTO Enrolled VALUES ('53650', 'Topology112', 'A'); INSERT INTO Enrolled VALUES ('53666', 'History105', 'B');

17. Practice 2 2. 각각의 referential integrity enforcement 에 따라 Students 의 레코드를 삭제한다. (NO ACTION, CASCADE) 3. 결과 메시지 혹은 삭제 후 테이블의 전체 내용들 을 확인한다.

18. Practice 2 TAs want to see query results… –NO ACTION enforcement –CASCADE

19. Constraint Check Confirm constraints on the tables. –Use a system table, user_constraints. SQL> SELECT table_name, constraint_name, constraint_type FROM user_constraints WHERE table_name = ‘your table name’; SQL> SELECT table_name, constraint_name, constraint_type FROM user_constraints