April 2002 Information Systems Design John Ogden & John Wordsworth 1 Database Design SQL (1) John Wordsworth Department of Computer Science The University of Reading Room 129, Ext 6544

April 2002 Information Systems Design John Ogden & John Wordsworth 2 Lecture objectives Outline the history of SQL. Distinguish data definition, data manipulation, and data control languages. Use SQL to perform projections and selections on tables. Use the COUNT, GROUP, and ORDER BY options of SQL SELECT. Use SQL for Cartesian product and equijoin. List the column aggregate functions and their uses.

April 2002 Information Systems Design John Ogden & John Wordsworth 3 Overview of SQL Language invented in IBM in the 1970s to support relational databases, and now an international standard. Three aspects: A Data Definition Language A Data Manipulation Language SELECT UPDATE INSERT DELETE A Data Control Language

April 2002 Information Systems Design John Ogden & John Wordsworth 4 Book Tables used throughout the SQL slides (1)

April 2002 Information Systems Design John Ogden & John Wordsworth 5 Publisher Qty Tables used throughout the SQL slides (2)

April 2002 Information Systems Design John Ogden & John Wordsworth 6 SQL : DDL Most important commands: CREATE TABLE CREATE INDEX ALTER TABLE DROP TABLE DROP INDEX CREATE TABLE Book ( IDINTEGERNOT NULL, TitleCHARACTER (35)NOT NULL, AuthorCHARACTER (25)NOT NULL, SubjectCHARACTER (25)NOT NULL ) ; ALTER TABLE Book ADD Bind CHARACTER (1) NOT NULL;

April 2002 Information Systems Design John Ogden & John Wordsworth 7 SELECT syntax SELECT [ DISTINCT | ALL ] { * | column_expression [ AS newname ] [,... ] } FROM table_name [ alias ] [,... ] [ WHERE condition ] [ GROUP BY column_list ] [ HAVING condition ] [ ORDER BY column_list ] ;

April 2002 Information Systems Design John Ogden & John Wordsworth 8 Projection SELECT * FROM Book ; denotes the whole table Book. SELECT DISTINCT Title FROM Book ; denotes the following table:

April 2002 Information Systems Design John Ogden & John Wordsworth 9 SELECT DISTINCT Title, Author FROM Book WHERE Subject = ‘Databases’; Selection

April 2002 Information Systems Design John Ogden & John Wordsworth 10 Using COUNT and GROUP BY SELECT Subject, COUNT(*) AS SCount FROM Book GROUP BY Subject ;

April 2002 Information Systems Design John Ogden & John Wordsworth 11 Using ORDER BY SELECT ID, Title, Author, Bind FROM Book WHERE Subject = ‘Databases’ ORDER BY ID ;

April 2002 Information Systems Design John Ogden & John Wordsworth 12 Cartesian product SELECT Book.*, Qty.* FROM Book, Qty ; denotes the Cartesian product of Book and Qty, 7 columns and 64 rows.

April 2002 Information Systems Design John Ogden & John Wordsworth 13 Equijoin with projection SELECT Title, Bind, No FROM Book, Qty WHERE Book.ID = Qty.ID ;

April 2002 Information Systems Design John Ogden & John Wordsworth 14 SELECT ID, Title, Author FROM Book, Publisher WHERE Book.ID = Publisher.ID AND Publisher.Pub_Name = ‘Addison Wesley’ ORDER BY Author; Equijoin with selection

April 2002 Information Systems Design John Ogden & John Wordsworth 15 SELECT Pub_Name, SUM(Qty.No) FROM Publisher, Qty WHERE Publisher.ID = Qty.ID GROUP BY Pub_Name HAVING SUM (Qty.No) > 1 Equijoin with other conditions

April 2002 Information Systems Design John Ogden & John Wordsworth 16 COUNT: the number of elements in each group SUM: the sum of the numeric values of an attribute in a group AVG: the average of the numeric valued of an attribute in a group MAX: the greatest numeric value of an attribute in a group MIN: the least numeric value of an attribute in a group Column aggregate functions

April 2002 Information Systems Design John Ogden & John Wordsworth 17 Key points SQL has been developed over many years, and is now an international standard. SQL provides commands for defining databases and tables, for making queries and updates, and for creating views and setting security options. The SELECT statement is used for projection, selection, Cartesian product, and equijoin. The column aggregate functions are COUNT, SUM, AVG, MIN, MAX; they need a GROUP BY clause to fix their scope.