Maintaining Referential Integrity Pertemuan 2 Matakuliah: T0413/Current Popular IT II Tahun: 2007

2 AGENDA: Constraining the Values of Data Maintaining Referential Integrity Entering, Deleting, and Changing Data Book: Mastering SQL by Martin Gruber Sybex (2000) Chapter : 4 – 6

3 Constraining the Values of Data Declaring constraints – Values that can be entered into its columns on a table – SQL will generally reject any values that violate the criteria you created before Syntax: CREATE TABLE tablename ({columnname datatype column constraint} …, [table constraint (columnname,…),…]; Alternative : ALTER TABLE

4 Constraining the Values of Data (cont’d) Using Constraints to Exclude NULLs – To prevent a column from permitting NULLs as a value – Use CREATE TABLE statement with NOT NULLs constraint Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL, sname CHAR(10) NOT NULL, city CHAR(10), comm DECIMAL); Column with NOT NULL constraint must be assigned values in every INSERT clause.

5 Constraining the Values of Data (cont’d) Specifying the Primary Key Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL, city CHAR(10), comm DECIMAL); Primary Keys of More Than One Column Example: CREATE TABLE Namefield (firstname CHAR(10) NOT NULL, lastname CHAR(10) NOT NULL, city CHAR(10), PRIMARY KEY (firstname, lastname));

6 Constraining the Values of Data (cont’d) Making Sure Values Are Unique – Using UNIQUE constraint – UNIQUE vs. PRIMARY KEY: PRIMARY KEY constraint can only be used on one column or group of columns. UNIQUE constraint may be used any number of times. PRIMARY KEY column may not contain NULLs, UNIQUE constraint may. – Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL UNIQUE, city CHAR(10), comm DECIMAL);

7 Constraining the Values of Data (cont’d) Checking Column Values – Using CHECK to Predetermine Valid Input Values – Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL, city CHAR(10) CHECK, (city IN (‘London’, ‘New York’, ‘San Jose’, ‘Barcelona’)), comm DECIMAL CHECK (comm < 1)); – Check Conditions Based on Multiple Columns – Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL UNIQUE, city CHAR(10), comm DECIMAL, CHECK (comm <.15 OR city = ‘Barcelona’));

8 Constraining the Values of Data (cont’d) Naming and Dropping Constraints Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL UNIQUE, city CHAR(10), comm DECIMAL, CONSTRAINT LuckyBarcelona CHECK (comm <.15 OR city = ‘Barcelona’)); Dropping constraints: ALTER TABLE Salespeople DROP CONSTRAINT LuckyBarcelona;

9 Constraining the Values of Data (cont’d) Assigning Default Values Example: CREATE TABLE Salespeople (snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL, city CHAR(10) DEFAULT = ‘New York’, comm DECIMAL CHECK (comm < 1)); Default Values and NULLs

10 Maintaining Referential Integrity Foreign Key and Parent Key Declaring Columns As Foreign Key: 1. FOREIGN KEY as a table constraint CREATE TABLE Customers (cnum INTEGER NOT NULL PRIMARY KEY, cname CHAR(10), city CHAR(10), snum INTEGER, FOREIGN KEY (snum) REFERENCES Salespeople(snum)); Note: Customers table with snum defined as a foreign key referencing the Salespeople table.

11 Maintaining Referential Integrity (cont’d) 2. FOREIGN KEY as a column constraint CREATE TABLE Customers (cnum INTEGER NOT NULL PRIMARY KEY, cname CHAR(10), city CHAR(10), snum INTEGER REFERENCES Salespeople(snum)); Note: Customers table with snum as a foreign key whose parent key is Salespeople.snum. It is equivalent to this table constraint: FOREIGN KEY (snum) REFERENCES Salespeople (snum)

12 Maintaining Referential Integrity (cont’d) 3. Using FOREIGN KEY to predetermined valid input values CREATE TABLE Officecities (office (CHAR(10) NOT NULL PRIMARY KEY); CREATE TABLE Salespeople ( snum INTEGER NOT NULL PRIMARY KEY, sname CHAR(10) NOT NULL, city CHAR(10) REFERENCES Officecities, comm DECIMAL CHECK (comm < 1));

13 Maintaining Referential Integrity (cont’d) PRIMARY vs. UNIQUE Parent Keys Multicolumn Foreign Keys Referential Triggered Actions : – how parent-key changes affect foreign keys – It enable you to specify when creating a FOREIGN KEY constraint what you would like to have happen to the foreign-key values when the referenced parent-key values are deleted or changed. – UPDATE : what happens to a foreign key value when the parent key value it references is changed. – DELETE : what happens to a foreign key value when the parent key row it references is deleted. – Solutions : CASCADE, SET NULL, SET DEFAULT, NO ACTION

14 Entering, Deleting, and Changing Data The INSERT statement Entering values into tables Syntax: INSERT INTO table name VALUES (value,…); Example: INSERT INTO Salespeople VALUES (1001, ‘Peel’, ‘London’,.12); Inserting NULLs value INSERT INTO Salespeople VALUES (1001, ‘Peel’, NULL,.12);

15 Entering, Deleting, and Changing Data (cont’d) Naming columns for INSERT INSERT INTO Customers (city, cname, cnum) VALUES (‘London’, ’Hoffman’, 2001); Inserting the Result of a Query INSERT INTO Londonstaff SELECT * FROM Salespeople WHERE city = ‘London’; INSERT INTO Londonstaff SELECT snum, sname, city, comm * 1.1 FROM Salespeople WHERE city = ‘London’;

16 Entering, Deleting, and Changing Data (cont’d) The DELETE statement Removing Rows from tables DELETE FROM Salespeople; DELETE FROM Salespeople WHERE snum = 1003; DELETE FROM Salespeople WHERE city = ‘London’;

17 Entering, Deleting, and Changing Data (cont’d) The UPDATE Statement Changing field values Example: UPDATE Customers SET rating = 200; Updating only certain rows UPDATE Customers SET rating = 200 WHERE snum = 1001;

18 Entering, Deleting, and Changing Data (cont’d) Updating multiple columns at once UPDATE Salespeople SET sname = ‘Gibson’, city = ‘Boston’, comm =.10 WHERE snum = 1004; Using value expression in UPDATE UPDATE Salespeople SET comm = comm * 2 WHERE city = ‘London’; Updating to NULL value UPDATE Customers SET rating = NULL Where city = ‘London’;

19 End of Maintaining Referential Integrity Thank you