OUTLINE OF THE LECTURE

PART I GOAL: Understand the Data Definition Statements in Fig 4.1 Step1: Columns of the Tables and Data types.Step2: Single column constraints:

Not Null; Default and; Unique Step3: Multi-column constraints:

Primary key Foreign key Step 4: Business process constraints (Check constraints)

PART II GOAL: Introduction to SQL LanguageUnrestricted results

Unordered or Ordered. Projection on certain specific columns of table.

Restricted results using ‘where clause’

STEP 1: COLUMNS OF THE TABLES AND DATA TYPES

Create Table Employee(

Fname Varchar(15), Minit Char, Lname Varchar(15), Ssn Char(9), Bdate Date, Address Varchar(30), Sex Char, Salary Decimal(10,2), Super_ssn char(9), Dno INT);

Create Table Department( Dname Varchar(15), Dnumber INT, Mgr_ssn char(9), Mgr_start_date Date);

STEP 1: COLUMNS OF THE TABLES AND DATA TYPES

Create Table Dependent( Essn Char(9),

Dependent_name Varchar(15), Sex Char, Bdate Date, Relationship Varchar(8));

• Downside: Poor quality data might get entered into the database. E.g.

• Too many NULLs are possible. • Duplicate entries of employees and departments.

Create Table Employee( Fname Varchar(15) NOT NULL, Minit Char, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Bdate Date, Address Varchar(30), Sex Char, Salary Decimal(10,2), Super_ssn char(9), Dno INT NOT NULL DEFAULT 9);

Create Table Department( Dname Varchar(15) NOT NULL, Dnumber INT NOT NULL, Mgr_ssn char(9) NOT NULL DEFAULT 123459999, Mgr_start_date Date, Unique (Dname));

Sometime we may want use default values for some fields to maintain consistency

STEP2: SINGLE COLUMN CONSTRAINTS:

Not NULL constraint help us to maintain data quality.

Ensure each Dname is Unique, No duplicates are allowed

Create Table Employee( Fname Varchar(15) NOT NULL, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Super_ssn char(9), Dno INT NOT NULL DEFAULT 9, Primary Key (Ssn));

Create Table Department( Dname Varchar(15) NOT NULL, Dnumber INT NOT NULL, Mgr_ssn char(9) NOT NULL DEFAULT 123459999, Mgr_start_date Date,

Primary Key (Dnumber), Unique (Dname) );

• Primary Key Vs Unique Constraint

• Primary Key can also defined as Unique + Not Null Constraint

• Many DBMS build an index on Primary Key (main advantage)

STEP 3: MULTI-COLUMN CONSTRAINT: PRIMARY KEY

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY

• Ref: Elmasari, Navathe, “Fundamentals of Database Systems” 6th edition

Create Table Employee( Fname Varchar(15) NOT NULL, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Super_ssn char(9), Dno INT NOT NULL DEFAULT 9, Primary Key (Ssn), Foreign Key (Super_ssn) References Employee (Ssn), Foreign Key (Dno) References Department (Dnumber));

Create Table Department( Dname Varchar(15) NOT NULL, Dnumber INT NOT NULL, Mgr_ssn char(9) NOT NULL DEFAULT 123459999, Mgr_start_date Date, Primary Key (Dnumber), Unique (Dname), Foreign Key (Mgr_ssn) References Employee (Ssn) );

• Need to be careful while putting the constraints.

• Otherwise data entry becomes hard.

• Does this schema create any trouble?• Circular reference Employee and

Department refer to each other• Consider adding some

constraints later using ALTER Table command

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY

Create Table Employee( Fname Varchar(15) NOT NULL, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Super_ssn char(9), Dno INT NOT NULL DEFAULT 9, Primary Key (Ssn), Foreign Key (Super_ssn) References Employee (Ssn),

Foreign Key (Dno) References Department (Dnumber)On Delete On Update

);• SET NULL • SET DEFAULT• CASCADE• RESTRICT/ NO

ACTION

• SET NULL • SET DEFAULT• CASCADE• RESTRICT/ NO

ACTION

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY (SET NULL/DEFAULT)

• SET NULL: sets the value of the referenced column to NULL • SET DEFAULT: Sets the value of the referenced column to the DEFAULT

Value

Create Table Employee( Fname Varchar(15) NOT NULL, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Super_ssn char(9), Dno INT NOT NULL DEFAULT 1, Primary Key (Ssn), Foreign Key (Super_ssn) References Employee (Ssn), Foreign Key (Dno) References Department (Dnumber)

On Delete SET DEFAULT On Update SET NULL);

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY (SET NULL/DEFAULT)

• What rows in Employee table are modified when Dnumber = 5 is deleted• What rows in Employee table modified when Dnumber = 1 is changed to

Dnumber = 3

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY (RESTRICT VS CASCADE)

• CASCADE: cascades the effect to tuple containing the foreign key:• For e.g. When used with on delete, if the tuple containing the referenced key

is delete, then all the tuples with that foreign key are also deleted. • RESTRICT: Produces an error indicating that the deletion or updating can violate a

foreign key constraint.

Create Table Employee( Fname Varchar(15) NOT NULL, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Super_ssn char(9), Dno INT NOT NULL DEFAULT 1, Primary Key (Ssn), Foreign Key (Super_ssn) References Employee (Ssn)

On Delete RESTRICT On Update CASCADE, Foreign Key (Dno) References Department (Dnumber));

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY (RESTRICT VS CASCADE)

• What happens when record of Employee ‘Franklin Wong’ is deleted ?• What happens when SSN of Employee ‘James Borg’ is updated to ‘888665599’ ?

• Ref: Elmasari, Navathe, “Fundamentals of Database Systems” 6th edition

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY: EXERCISE

STEP 3: MULTI-COLUMN CONSTRAINT: FOREIGN KEY EXERCISE Create Table Department( Dname Varchar(15) NOT NULL, Dnumber INT NOT NULL, Mgr_ssn char(9) NOT NULL, Mgr_start_date Date, Primary Key (Dnumber), Unique (Dname), Foreign Key (Mgr_ssn) References Employee (Ssn) );

Create Table Project( Pname Varchar(15) NOT NULL, Pnumber INT NOT NULL, Plocation Varchar(15), Dnum INT, Primary Key (Pnumber), Foreign Key (Dnum) References Department (Dnumber)

On Delete Cascade On Update Cascade );

Create Table Works_on( Essn char(9) NOT NULL, Pno INT NOT NULL, Hours Decimal (3,1) NOT NULL, Primary Key (Essn,Pno), Foreign Key (Essn) References Employee(ssn), Foreign Key (Pno) Reference Project(Pnumber)

On Delete Cascade On Update Cascade );

• Identify the affected rows when record with Dnumber =4 is deleted

Create Table Employee( Fname Varchar(15) NOT NULL, Minit Char, Lname Varchar(15) NOT NULL, Ssn Char(9) NOT NULL, Bdate Date, Address Varchar(30), Sex Char, Salary Decimal(10,2), Super_ssn char(9), Dno INT NOT NULL DEFAULT 9, Constraint EMPSAL Check (Salary > 0.0));

Create Table Department( Dname Varchar(15) NOT NULL, Dnumber INT NOT NULL, Dept_create_date Date NOT NULL, Mgr_ssn char(9) NOT NULL DEFAULT 123459999, Mgr_start_date Date, Constraint MGRDATE Check (Dept_create_date <= Mgr_start_date));

Step 4: Business process constraints (Check constraints)

Check constraints for maintaining the sanity of data

OUTLINE OF THE LECTURE

PART I GOAL: Understand the Data Definition Statements in Fig 4.1 Step1: Columns of the Tables and Data types.Step2: Single column constraints:

Not Null; Default and; Unique Step3: Multi-column constraints:

Primary key Foreign key Step 4: Business process constraints (Check constraints)

PART II GOAL: Introduction to SQL LanguageUnrestricted results

Unordered or Ordered. Projection on certain specific columns of table.

Restricted results using ‘where clause’

“Hello world” example in SQL Language:

SELECT * <specify the columns to be extracted>

FROM Employee; <specify the Tables to read> ; <Optional where clause>

<Optional order by clause>

Outputs the entire contents of the Table Employee

Ordered results:

SELECT *

FROM Employee

ORDER BY Lname ASC;

Outputs the entire contents of Employee ordered (in ascending order) on last name. DESC -> descending order Can give multiple column names e.g. ORDER BY Lname ASC, Fname ASC

Part II: Introduction to SQL Language: Unrestricted Results

Projected only few columns in SQL Language:

SELECT Ssn, Bdate, Address

FROM Employee;

Outputs the Ssn, Bdate and Address columns of Employee

Ordered results:

SELECT Lname, Ssn, Dno

FROM Employee

ORDER BY Lname ASC;

Outputs the Lname, Ssn and Dno of Employee ordered (in ascending order) on last name.

Part II: Introduction to SQL Language: Unrestricted Results with Projection

Part II: Introduction to SQL Language: Restricted Results using where Clause

Can use where clause to filter some unnecessary results: For instance if we only need the details of employees from Dept no 5

SELECT * FROM Employee

WHERE Dno = 5; <selection condition>

Outputs all the details of employees belonging to Dept no 5 Other logical comparators in SQL: < , <= , >, >= , <> Use ‘AND’ for conjunction of multiple conditions inside a where clause.

SELECT * FROM Employee

WHERE Dno = 5 AND Salary >100000;

Part II: Introduction to SQL Language: Restricted Results: Substring Pattern Matching

Use the ‘LIKE’ comparison operator to specify comparison operations on only parts of the string.

SELECT Fname, Lname FROM Employee

WHERE Address LIKE ‘%Minneapolis,MN %’;

Retrieves the employees who live in Minneapolis, MN % Arbitrary number of zero or more characters. _ Replaces with a single charector. \ Escape character for using _ and % as a literal character. “ Escape character for single quotation (‘).