An Introduction to SQL

1. An Introduction to SQL Kirk AnneComputing & Information Technology SUNY Geneseo kma@geneseo.edu Nael Alian naelalian@yahoo.com

2. What is a database?

3. Parts of a database • Attributes (fields) • An attribute or field is a component of a record that describes something about an item. • Records • A record is the representation of an individual item. • Table • A collection of records • Database • A collection of tables and rules for accessing the tables

4. Parts of a database Record Tables Attribute/Field • Records become “rows” • Attributes/fields become “columns” • Rules determine the relationship between the tables and tie the data together to form a database

5. I need a new database! • Many people ask for “new databases” when in fact they only need a new table within an existing database. • The data within the tables should be all related somehow. • By owner • By project

6. Creating a database • What information are we trying to store? • How do we describe the information? • Phone Book/Contact entries • Name • Address • Company • Phone Number • URL/Web Page • Age • Height (in meters) • Birthday • When we added the entry

7. Data Types • Binary • Database specific binary objects • Pictures, digital signatures, etc. • Boolean • True/False values • Character • Fixed width or variable size • Numeric • Integer, Real (floating decimal point), Money • Temporal • Time, Date, Timestamp

8. Phone Book/Contact Record Name Character Address Character Company Character Phone Number Character URL/Web Page Character Age Integer Height Real (float) Birthday Date When we added the entry Timestamp

9. All you need to know about SQL

10. 1. SQL stands for Structured Query Language2. SQL lets you access and manipulate databases3. SQL is an ANSI (American National Standards Institute) standard What is SQL?

11. What Can SQL do? • SQL can execute queries against a database • SQL can retrieve data from a database • SQL can insert records in a database • SQL can update records in a database • SQL can delete records from a database • SQL can create new databases • SQL can create new tables in a database • SQL can create stored procedures in a database • SQL can create views in a database • SQL can set permissions on tables, procedures, and views

12. SQL DML and DDL SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL). The query and update commands form the DML part of SQL: SELECT - extracts data from a database UPDATE - updates data in a database DELETE - deletes data from a database INSERT INTO - inserts new data into a database

13. The DDL part of SQL permits database tables to be created or deleted. It also define indexes (keys), specify links between tables, and impose constraints between tables. The most important DDL statements in SQL are: CREATE DATABASE - creates a new database ALTER DATABASE - modifies a database CREATE TABLE - creates a new table ALTER TABLE - modifies a table DROP TABLE - deletes a table CREATE INDEX - creates an index (search key) DROP INDEX - deletes an index

14. Basic SQL Commands • Creating tables with CREATE • Adding data with INSERT • Viewing data with SELECT • Removing data with DELETE • Modifying data with UPDATE • Destroying tables with DROP

15. Creating tables with CREATE • Generic form CREATE TABLE tablename ( column_name data_type attributes…, column_name data_type attributes…, … ) • Table and column names can’t have spaces or be “reserved words” like TABLE, CREATE, etc.

16. Phone Book/Contact Record Name Character Address Character Company Character Phone Number Character URL/Web Page Character Age Integer Height Real (float) Birthday Date When we added the entry Timestamp

17. Phone Book/Contact Table CREATE TABLE contacts ( Name VARCHAR(40), Address VARCHAR(60), Company VARCHAR(60), Phone VARCHAR(11), URL VARCHAR(80), Age INT, Height FLOAT, Birthday DATE, WhenEntered TIMESTAMP ); Plan your tables very carefully! Once created, they are difficult to change!

18. Phone Book/Contact Table CREATE TABLE contacts ( ContactID INT PRIMARY KEY, Name VARCHAR(40), Address VARCHAR(60), Company VARCHAR(60), Phone VARCHAR(11), URL VARCHAR(80), Age INT, Height FLOAT, Birthday DATE, WhenEntered TIMESTAMP ); If you are going to use the relational nature of a database,don’t forget you need to have a unique way to access records! There is a way to make the key automatically increment,so you don’t have to worry about which one is next.

19. Data Types • Binary • Database specific binary objects (BLOB) • Boolean • True/False values (BOOLEAN) • Character • Fixed width (CHAR) or variable size (VARCHAR) • Numeric • Integer (INT), Real (FLOAT), Money (MONEY) • Temporal • Time (TIME), Date (DATE), Timestamp (TIMESTAMP)

21. Adding data with INSERT • Generic Form INSERT INTO tablename (column_name,…) VALUES (value,…)

22. Inserting a record into ‘contacts’ INSERT INTO contacts (contactid,name,address,company,phone,url,age,height,birthday,whenentered) VALUES (1,‘Joe’,’123 Any St.’,’ABC’, ’800-555-1212’,‘http://abc.com’,30,1.9,’6/14/1972’,now());

23. Inserting a partial record INSERT INTO contacts (contactid,name,phone) VALUES (2,’Jane’,’212-555-1212’);

24. Automatic key generation • CREATE SEQUENCE contactidseq; • Change the ContactID line in the CREATE TABLE to: ContactID INT DEFAULT nextval(‘contactidseq’) PRIMARY KEY • Or when inserting into a table INSERT contacts (contactid,name,phone) VALUES (nextval(‘contactidseq’),’Jack’, ‘716-555-1212’);

26. Viewing data with SELECT • Generic Form SELECT column,… FROM table,… WHERE condition GROUP BY group_by_expressionHAVING condition ORDER BY order_expression • The most used command • Probably the most complicated also • If used improperly, can cause very long waits because complex computations

27. A few simple SELECTs • SELECT * FROM contacts; • Display all records in the ‘contacts’ table • SELECT contactid,name FROM contacts; • Display only the record number and names • SELECT DISTINCT url FROM contacts; • Display only one entry for every value of URL.

29. Refining selections with WHERE • The WHERE “subclause” allows you to select records based on a condition. • SELECT * FROM contacts WHERE age<10; • Display records from contacts where age<10 • SELECT * FROM contacts WHERE age BETWEEN 18 AND 35; • Display records where age is 18-35

30. Additional selections • The “LIKE” condition • Allows you to look at strings that are alike • SELECT * FROM contacts WHERE name LIKE ‘J%’; • Display records where the name starts with ‘J’ • SELECT * FROM contacts WHERE url LIKE ‘%.com’; • Display records where url ends in “.com”

32. Removing data with DELETE • Generic Form DELETE FROM table WHERE condition; DELETE FROM contacts WHERE age<13;

34. Modifying data with UPDATE • Generic Form UPDATE table SET column=expression WHERE condition; UPDATE contacts SET company=‘AOL’ WHERE company=‘Time Warner’;

35. Destroying tables with DROP • Generic Form DROP TABLE tablename; DROP TABLE contacts;

36. More about SELECT

37. Different types of JOINs • “Inner Join” • Unmatched rows in either table aren’t printed • “Left Outer Join” • All records from the “left” side are printed • “Right Outer Join” • All records from the “right” side are printed • “Full Outer Join” • All records are printed • Multiple Table Join • Join records from multiple tables

38. General form of SELECT/JOIN SELECT columns,… FROM left_table join_type JOIN right_table ON condition; SELECT name,phone FROM people JOIN phonenumbers ON people.id=phonenumbers.id;

39. Other versions SELECT name,phone FROM people LEFT JOIN phonenumbers ON people.id=phonenumbers.id; SELECT name,phone FROM people RIGHT JOIN phonenumbers ON people.id=phonenumbers.id; SELECT name,phone FROM people FULL JOIN phonenumbers ON people.id=phonenumbers.id;

40. “Theta style” vs. ANSI • Theta Style (used in most SQL books) SELECT name,phone,zip FROM people, phonenumbers, address WHERE people.addressid=address.addressid AND people.id=phonenumbers.id; • ANSI Style uses JOIN SELECT name,phone,zip FROM people JOIN phonenumbers ON people.id=phonenumbers.id JOIN address ON people.addressid=address.addressid;

41. Other SELECT examples • SELECT * FROM contacts WHERE name is NULL; • SELECT * FROM contacts WHERE zip IN (‘14454’,’12345’); • SELECT * FROM contacts WHERE zip IN ( SELECT zip FROM address WHERE state=‘NY’ );

42. GROUP BY/HAVING • The “GROUP BY” clause allows you to group results together with “aggregate functions” • AVG(), COUNT(), MAX(), MIN(), SUM() • COUNT DISTINCT • HAVING allows you to search the GROUP BY results

43. GROUP BY Examples SELECT company,count(company)FROM contactsGROUP BY company; SELECT company,count(company)FROM contactsGROUP BY companyHAVING count(company) > 5;

44. ORDER BY • The “ORDER BY” clause allows you to sort the results returned by SELECT. SELECT * FROM contacts ORDER BY company; SELECT * FROM contacts ORDER BY company, name;

45. Views • You can use “CREATE VIEW” to create a virtual table from a SELECT statement. CREATE VIEW contactview AS (SELECT name,phone,zip FROM people,phonenumbers,address WHERE people.id=phonenumbers.id AND people.addressid=address.addressid);