Introduction to Databases

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1 Introduction to Databases Abou Bakar Kaleem 1 Overview - Database - Relational Databases - Introduction to SQL Introduction to Databases 2 1

2 Database (1) Database : - is a collection of related data - represents some aspects of the real world - is designed built and populated with data for a specific purpose Data: - known facts that can be recorded and that have implicit meaning Introduction to Databases 3 Database (2) Examples: - A manufacturing company.product Data - A bank.account Data - A hospital Patient Data - A university Student Data - A government department Planning Data Introduction to Databases 4 2

3 Database (3) -Defining a database involves specifying the data types, structures and constraints for the data to be stored in the database - Constructing a database is the process of storing the data itself on some storage medium - Manipulating a database includes such functions as querying the database to retrieve specific data, updating the database to reflect changes and generating reports from the data Introduction to Databases 5 Database (4) Database Management System (DBMS): - is a general purpose software system that enables users to define,construct and manipulate a database Database System: - The database itself and the software together is called database system Introduction to Databases 6 3

4 Simplified DB System Environment Users / Programmers Database System Applications / Queries Software to process queries & App Software to access stored data DBMS Meta Data Database Introduction to Databases 7 Why Database? - Compactness: No need for possibly voluminous paper files - Speed: The machine can retrieve and change data far faster than a human can - Potential for enforcing standards - Reduced application development time - Availability of up-to-date information - Complex relationships among data Introduction to Databases 8 4

5 Characteristics of Databases - Controlling redundancy - Restricting unauthorized access - Enforcing integrity constraints - Providing multiple user interfaces - Avoiding inconsistency - Providing back up and recovery Introduction to Databases 9 Relational Database (1) - is a database that presents data to its users (end users, analysts and programmers) as a set of relations (also known as Tables) Relation: - is made up of a relation name and a list of attributes e.g STUDENT (Name, Mat.No, Home Phone, Address, GPA) CUSTOMER (Account No, Name, Add, Credit Limit, Balance) Introduction to Databases 10 5

6 Relational Database (2) - Relations are represented as Tables and tables consist of rows and columns - Every row represents a relation instance and is called a Tuple - Number of rows in a table is called Cardinality of relation - Columns of the table are the attributes of the relation - Number of the columns in a table is called Degree of a relation Introduction to Databases 11 Example: Invoice Tuples Inv. No Account No Invoice Date Amount (DM) Introduction to Databases 12 6

7 Relational Database (3) Examples: STUDENT (Name, Mat.No, Home Phone, Address, GPA) Degree of relation = 5 CUSTOMER (Account No, Name, Address, Credit Limit, Balance) Degree of relation = 5 INVOICE (Invoice No, Account No, Invoice Date, Amount) Degree of relation = 4 Introduction to Databases 13 Relational Database (4) Primary Key (PK): - No two rows in a relational database are allowed to be identical - A subset (often one) of the attributes is chosen as the PK - The PK value is unique to each row STUDENT (Name, Mat.No, Home Phone, Address, GPA) CUSTOMER (Account No, Name, Address, Credit Limit, Balance) Introduction to Databases 14 7

8 Relational Database (5) - PK that consists of just one attribute are called Atomic PK - Composite or Compound PK consists of more than one attribute CUSTOMER (Account No, Name, Address, Credit Limit, Balance) CUSTOMER (Account No, Name, Address, Credit Limit, Balance) Candidate Key: - is a set of one or more attributes that is suitable for use as the PK Introduction to Databases 15 Relational Database (6) FOREIGN KEY (FK): - FK values show relationships between table rows - A FK in one table is a PK in some other table Examples: CUSTOMER (Account No, Name, Address, Credit Limit, Balance) INVOICE (Invoice No, ACCOUNT NO, Invoice Date, Amount) Introduction to Databases 16 8

9 Relational Database (7) CONSTITUENCY (Cons.No, Name, Town Hall Address) CANDIDATE (Candidate No, CONS.NO, PARTY NO, Name, Age) PARTY (Party No, Party Name, Party Chair) Introduction to Databases 17 Entity Integrity Constraint - states that no PK values can be NULL What does NULL mean? - It can mean that property does not apply or unknown - It denotes nothing Why NULL is necessary? - The use of NULL can arise in relational databases e.g maternity leave date for a male employee Introduction to Databases 18 9

10 Referential Integrity Constraint (1) - states that a tuple in one relation that refers to another relation must refer to an existing tuple - is specified between two relations and is used to maintain the consistency among tuples of the two relations - The conditions for a FK specify a referential integrity constraint between the two relations Introduction to Databases 19 Referential Integrity Constraint (2) Example: CUSTOMER (Account No, Name, Add, Credit Limit, Balance) 1, Sandra, 25 Moor St, 1500, 725,85 2, Mike, 19 Alster St, 1200, 675,93 INVOICE (Invoice No, Account No, Invoice Date, Amount) 10, 1, , , 1, , , 3, , , 2, , Referential integrity constraint is broken! Introduction to Databases 20 10

11 Introduction to SQL (1) - SQL (Structured Query Language) is used for accessing databases - Variation of SQL have been implemented by most commercial DBMS vendors - A standard called SQL2 (1992) has been developed by ANSI and ISO (SQL1 in 1986) - Plans are underway for SQL3 with object oriented database concepts - SQL has statements for data definition, query and update - SQL uses terms Table, Row and Column for Relation, Tuple and Attribute respectively Introduction to Databases 21 Introduction to SQL (2) The SQL CREATE TABLE command The basic syntax forms of the CREATE TABLE command is: CREATE TABLE table-name (column-name data type [ NULL NOT NULL ],... ) CREATE TABLE table-name (column-name [NOT NULL],... ) AS query Introduction to Databases 22 11

12 Introduction to SQL (3) Example: CREATE TABLE Customer ( Account No NUMBER (8), Name CHAR (20), Address CHAR (20), Credit Limit NUMBER (5, 0), Balance NUMBER (7, 2)) ; Introduction to Databases 23 Introduction to SQL (4) Inserting rows into tables with INSERT: The syntax is: INSERT INTO table-name [ ( column-name,... ] VALUES ( value,... ) ; INSERT INTO table-name [ ( column-name,... ] query Introduction to Databases 24 12

13 Introduction to SQL (5) Example: INSERT INTO INVOICE Invoice NO, Account No, Invoice Date, Amount VALUES ( 1018, 2436, , ) ; Introduction to Databases 25 Introduction to SQL (6) Deleting rows from tables with DELETE: The syntax is: Example: DELETE FROM table-name [WHERE condition] ; DELETE FROM INVOICE WHERE Account No = 1 Introduction to Databases 26 13

14 Introduction to SQL (7) The SQL SELECT statement The basic syntax is: SELECT FROM WHERE attribute list table list condition Introduction to Databases 27 Introduction to SQL (8) Examples: SELECT Name, Address, GPA FROM STUDENT WHERE Mat.No < SELECT Account No, Name FROM INVOICE WHERE Amount > 500,00 Introduction to Databases 28 14

CS275 Intro to Databases

CS275 Intro to Databases The Relational Data Model Chap. 3 How Is Data Retrieved and Manipulated? Queries Data manipulation language (DML) Retrieval Add Delete Update An Example UNIVERSITY database Information