1. University of Sunderland COM 220Lecture Two Slide 1 Database Theory

2. University of Sunderland COM 220Lecture Two Slide 2 Objectives Understanding of relational data model Basic concepts of set theory Learn how to use SQL query language

3. University of Sunderland COM 220Lecture Two Slide 3 Devised by Codd in 1970, conforming to a simple set of rules – –Data stored as two dimensional tables (relations) – –Every relation must have a unique name – –Each column (attribute) has a unique name within a table – –Each value of an attribute is from the same domain – –Order of rows (tuples) is irrelevant – –Order of columns (attributes) is irrelevant – –Each value should be single-valued (atomicity) Relational Data Model

4. University of Sunderland COM 220Lecture Two Slide 4 Relational Database - Example BRANCH relation STAFF relation

5. University of Sunderland COM 220Lecture Two Slide 5 Keys Primary Key: –all tables have an attribute or set of attributes which uniquely identifies each separate row in the table –e.g. branchNo in BRANCH table –staffNo in STAFF table –Note that we could not use the staffName attribute as the primary key –why do you think this is?

6. University of Sunderland COM 220Lecture Two Slide 6 Keys Foreign Key: –a set of attributes in a table which match the primary key of some other table –e.g. branchNo in STAFF relation –Allows us to join tables together to relate information in tables.

7. University of Sunderland COM 220Lecture Two Slide 7 Relational Data Manipulation Codd’s definition of the relational model was based on a sound theoretical basis Set theory Allows us to specify relations between sets, e.g. –StaffNames = {‘John White’, ‘Ann Beech’, ‘David Ford’} –StaffSalaries = {30000, 12000, 18000}

8. University of Sunderland COM 220Lecture Two Slide 8 Relational Data Manipulation It is fine to be able to store data in a relational database But we also need to be able to retrieve from it too The use of set theory provides a basis for all relational query languages such as SQL Relational algebra contains operations for –RESTRICT - return rows satisfying condition –PROJECT - return specified columns –JOIN - join of two tables on primary key/foreign key

9. University of Sunderland COM 220Lecture Two Slide 9 Example Queries 1 SQL –select branchNo, city from branch; Relational Algebra This is use of PROJECT

10. University of Sunderland COM 220Lecture Two Slide 10 Example Queries 2 SQL: –select * from branch where branchNo = ‘B003’; Relational Algebra: –Use of RESTRICT

11. University of Sunderland COM 220Lecture Two Slide 11 Example Queries 3 SQL: –select branchNo,staff_forename, staff_surname from branch, staff where branch.branchNo = staff.branchNo; Relational Algebra: –Use of JOIN

12. University of Sunderland COM 220Lecture Two Slide 12 What is it? Historical Background Internal structure Commands SQL

13. University of Sunderland COM 220Lecture Two Slide 13 Originally called SEQUEL – –developed by IBM c1976 Now called SQL – –the ISO standard query language for relational databases DEVELOPED TO: – – Reduce programmers workload – – Make programs and data functionally independent – – Make data structures more flexible – – Allow end-user access to data Historical Background

14. University of Sunderland COM 220Lecture Two Slide 14 DIVIDED INTO 2 MAIN ELEMENTS Data Definition Language ( DDL ) Data Manipulation Language ( DML ) Internal Structure

15. University of Sunderland COM 220Lecture Two Slide 15 SYNTAX Commands may be on one or many lines Command words cannot be split SQL commands are not case sensitive Only one statement can be current within the SQL buffer SQL statements always end in a semi-colon ; SQL

16. University of Sunderland COM 220Lecture Two Slide 16 USED TO: define the structure of data (CREATE) which columns are in which tables what indexes are maintained change existing rows ( ALTER ) delete existing rows/tables ( DELETE) (DROP) grant/revoke access to ORACLE database & its structures Data Definition (DDL)

17. University of Sunderland COM 220Lecture Two Slide 17 USED TO: retrieve/query data SELECT insert dataINSERT delete dataDELETE protect dataGRANT Data Manipulation (DML)

18. University of Sunderland COM 220Lecture Two Slide 18 RETRIEVAL THE SELECT COMMAND The purpose of this command is to read data from the database and present it in user specified form. By far the most complex of all SQL commands, with the ability to perform a wide range of tasks. Data Manipulation (DML)

19. University of Sunderland COM 220Lecture Two Slide 19 Used when an SQL query requires data from more than one table in the database Rows in one table can be joined to rows in another according to common values. These common values are the primary key of one table and the foreign key of the other table Table Joins

20. University of Sunderland COM 220Lecture Two Slide 20 Adding/Removing Rows Use the INSERT or DELETE command Examples: INSERT INTO emp VALUES (1234, ‘Barney Rubble’, ‘Manager’, 30000); DELETE FROM emp WHERE job = ‘Administrator’;

21. University of Sunderland COM 220Lecture Two Slide 21 Protecting Data Use GRANT command to set privileges on data e.g. GRANT SELECT ON emp TO ALL; GRANT UPDATE ON emp TO personnel;

22. University of Sunderland COM 220Lecture Two Slide 22 Further Reading Relational Model –Connolly & Begg, 3 rd and 4 th edition, chapter 3 SQL –Connolly & Begg, 3 rd and 4 th edition, chapter 5 Next week: –Database Application Lifecycle