1. ITEC 3220A Using and Designing Database Systems Instructor: Prof. Z. Yang Course Website: http://people.yorku.ca/~zyang/itec 3220a.htm http://people.yorku.ca/~zyang/itec 3220a.htm Office: Tel 3049

2. Chapter 7 Introduction to Structured Query Language (SQL)

3. 3 Introduction to SQL SQL functions fit into two broad categories: –Data definition language SQL includes commands to create –Database objects such as tables, indexes, and views –Commands to define access rights to those database objects –Data manipulation language Includes commands to insert, update, delete, and retrieve data within the database tables

4. 4 Introduction to SQL (continued)

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7. 7 Creating the Database Two tasks must be completed –create the database structure –create the tables that will hold the end- user data

8. 8 Creating Table Structures Use one line per column (attribute) definition Use spaces to line up the attribute characteristics and constraints Table and attribute names are capitalized NOT NULL specification UNIQUE specification Primary key attributes contain both a NOT NULL and a UNIQUE specification RDBMS will automatically enforce referential integrity for foreign keys Command sequence ends with a semicolon

9. 9 Table Creation Steps Steps in table creation: 1.Identify data types for attributes 2.Identify columns that can and cannot be null 3.Identify columns that must be unique 4.Identify primary key-foreign key mates 5.Determine default values 6.Identify constraints on columns (domain specifications) 7.Create the table CREATE TABLE table name (attribute1 name and attribute1 characteristics, attribute2 name and attribute2 characteristics, attribute3 name and attribute3 characteristics, primary key designation, foreign key designation and foreign key requirement);

10. 10 Data Types

11. 11 An Example CREATE TABLE STUDENT( 2 STU_NUM INTEGER NOT NULL UNIQUE, 3 STU_NAME VARCHAR(15) NOT NULL, 4 GPA DECIMAL(3,2) NOT NULL, 5 PRIMARY KEY(STU_NUM)); Table created. Define attributes and their data types Semicolon indicates end of command Message indicates table was created Comma indicates end of description of an attribute Not null specifications Unique specifications Identify primary key

12. 12 SQL Integrity Constraints Adherence to entity integrity and referential integrity rules is crucial –Entity integrity enforced automatically if primary key specified in CREATE TABLE command sequence –Referential integrity can be enforced in specification of FOREIGN KEY –Other specifications to ensure conditions met: ON DELETE RESTRICT ON UPDATE CASCADE

13. 13 Advanced Data Definition Commands All changes in the table structure are made by using the ALTER command –Followed by a keyword that produces specific change –Three options are available ADD MODIFY DROP

14. 14 Changing a Column’s Data Type ALTER can be used to change data type Some RDBMSs (such as Oracle) do not permit changes to data types unless the column to be changed is empty

15. 15 Changing a Column’s Data Characteristics Use ALTER to change data characteristics If the column to be changed already contains data, changes in the column’s characteristics are permitted if those changes do not alter the data type

16. 16 Adding or Dropping a Column Use ALTER to add a column –Do not include the NOT NULL clause for new column Use ALTER to drop a column –Some RDBMSs impose restrictions on the deletion of an attribute

17. 17 Data Manipulation Commands Adding table rows Saving table changes Listing table rows Updating table rows Restoring table contents Deleting table rows Inserting table rows with a select subquery

18. 18 Common SQL Data Manipulation Commands

19. 19 Data Entry Enters data into a table INSERT INTO VALUES (attribute 1 value, attribute 2 value, … etc.);

20. 20 Listing Table Rows SELECT –Used to list contents of table Syntax –SELECT columnlist FROM tablename Columnlist represents one or more attributes, separated by commas Asterisk can be used as wildcard character to list all attributes

21. 21 Updating Table Rows UPDATE –Modify data in a table Syntax –UPDATE tablename SET columnname = expression [, columname = expression] [WHERE conditionlist]; If more than one attribute is to be updated in the row, separate corrections with commas

22. 22 Saving Table Changes Changes made to table contents are not physically saved on disk until –Database is closed –Program is closed –COMMIT command is used Syntax –COMMIT –Will permanently save any changes made to any table in the database

23. 23 Restoring Table Contents ROLLBACK –Used to restore the database to its previous condition –Only applicable if COMMIT command has not been used to permanently store the changes in the database Syntax –ROLLBACK; COMMIT and ROLLBACK only work with data manipulation commands that are used to add, modify, or delete table rows

24. 24 Deleting Table Rows DELETE –Deletes a table row Syntax –DELETE FROM tablename [WHERE conditionlist ]; WHERE condition is optional If WHERE condition is not specified, all rows from the specified table will be deleted

25. 25 Selecting Rows with Conditional Restrictions Select partial table contents by placing restrictions on rows to be included in output –Add conditional restrictions to the SELECT statement, using WHERE clause Syntax –SELECT columnlist FROM tablelist [ WHERE conditionlist ] ;

26. 26 Comparison Operators

27. 27 Arithmetic Operators: The Rule of Precedence Perform operations within parentheses Perform power operations Perform multiplications and divisions Perform additions and subtractions

28. 28 Special Operators BETWEEN –Used to check whether attribute value is within a range IS NULL –Used to check whether attribute value is null LIKE –Used to check whether attribute value matches a given string pattern IN –Used to check whether attribute value matches any value within a value list EXISTS –Used to check if a subquery returns any rows

29. 29 More Complex Queries and SQL Functions Listing unique values –DISTINCT clause produces list of different values Aggregate functions –Mathematical summaries SELECT DISTINCT V_CODE FROM PRODUCT;

30. 30 Example Aggregate Function Operations COUNT MAX and MIN SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT; SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT WHERE P_PRICE <= 10.00; SELECT MIN(P_PRICE) FROM PRODUCT; SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT WHERE P_PRICE = MAX(P_PRICE);

31. 31 Example Aggregate Function Operations (Cont’d) SUM AVG SELECT SUM(P_ONHAND * P_PRICE) FROM PRODUCT; SELECT P_DESCRIPT, P_ONHAND, P_PRICE, V_CODE FROM PRODUCT WHERE P_PRICE > (SELECT AVG(P_PRICE) FROM PRODUCT) ORDER BY P_PRICE DESC;

32. 32 More Complex Queries and SQL Functions (Cont’d) Ordering a listing Results ascending by default –Descending order uses DESC Cascading order sequence ORDER BY ORDER BY DESC ORDER BY

33. 33 More Complex Queries and SQL Functions (cont’d) Grouping data –Creates frequency distributions –Only valid when used with SQL arithmetic functions –HAVING clause operates like WHERE for grouping output SELECT P_SALECODE, MIN(P_PRICE) FROM PRODUCT_2 GROUP BY P_SALECODE; SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE) FROM PRODUCT_2 GROUP BY V_CODE HAVING AVG(P_PRICE) < 10;

34. 34 SQL Exercise Write SQL code that will create the relation shown below. Assume the following attribute data types: –Customer_ID: integer –Customer_Name: 25 characters –Street: 25 characters –City: 15 characters –State: 15 characters –Balance: number(8,2) –Credit_Limit: number(8,2) –Rep_Number: integer Customer (Customer_ID, Customer_Name, Street, City, State, Balance, Credit_Limit, Rep_Number)

35. 35 SQL Exercise (cont’d) Find the ID and name of each customer located in the city of Toronto. Find the ID and name for all customers with credit limits that exceed their balances. Find the ID, name and available credit (the credit limit minus balance) for each customer. Find the total number of customers and the total of their balances. For each sales rep, list the rep number and the average balance of the rep’s customers.

36. 36 Summary SQL commands can be divided into two overall categories: –Data definition language commands –Data manipulation language commands Basic data definition commands allow you to create tables, indexes, and views Many SQL constraints can be used with columns Aggregate functions –Special functions that perform arithmetic computations over a set of rows

37. 37 Summary ( Cont’d ) ORDER BY clause –Used to sort output of a SELECT statement –Can sort by one or more columns and use either an ascending or descending order Join output of multiple tables with SELECT statement Natural join uses join condition to match only rows with equal values in specified columns

38. 38 Lab Instruction Before you go to the lab sessions, please use your Passport York to create TEL lab account and AML account. These two accounts will allow you to get access to the ORACLE database. Please create these two accounts as early as possible since it takes time for these two accounts to take effect.

39. 39 Lab Instruction (cont’d) Login to sit.yorku.ca Start Oracle SQL*PLUS environment by typing the following command: sqlplus When prompted for the username/password enter your_username@studb10g (where your_username is your AML username) at the username prompt and your AML password at the password prompt.