1. Introduction to SQL
Wenhao Zhang
October 5, 2018

2. What is a Database(DB)? Any collection of related information
Shopping list
To do list
Database can be stored in different ways
On paper or in your mind
On a computer (Spreedsheet)
Computer is good at keeping track of large amounts of information

3. Database Management System(DBMS)
A special software program that helps users create and maintain a database(MySQL, Oracle, PostgreSQL, MariaDB, etc)
Make it easy to manage large amounts of information
Handles security
Backups
Importing/exporting data
Concurrency
Interacts with software apps(Programming language)

4. Types of Databases Relational Databases(SQL)
Organize data into one or more tables
Each tables has columns and rows
Non-Relational(noSQL/ not just SQL)
Organize data is anything but a traditional table
Graphs, Documents, etc

5. Structured Query Language(SQL)
SQL is a language used for interacting with Relational Database Management Systems
Create, retrieve, update & delete (C.R.U.D)
Create & manage databases
Design & create database tables
Perform administration tasks(security, import/export, user management, etc)

6. Structured Query Language(SQL)
Data Query Language (DQL)
Query the database for information
Data Definition Language (DDL)
Define database schemas
Data Control Language (DCL)
Control access to the data in the database
Data Manipulation Language (DML)
Insert, update and delete data from the database

7. Tables in SQL Table name Attribute names Product PName Price Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
rows

8. Keys and Foreign Keys Company Key Product Foreign key CName StockPrice
Country
GizmoWorks 25
USA
Canon 65
Japan
Hitachi 15
Key
Product
Foreign key
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi

9. Tables Explained
The schema of a table is the table name and its attributes:
Product(PName, Price, Category, Manfacturer)
A key is an attribute whose values are unique; we underline a key

10. Data Types in SQL SQL supports a large number of different formats
Numeric:
INT, BIGINT, SMALLINT
Character:
CHAR(L) : a fixed length character of length L
VARCHAR(L): a variable length character of length L
Date:
DATE(), TIME()

11. Important SQL commands
SELECT - extracts data from a database
UPDATE - updates data in a database
DELETE - delete data from a database
INSERT INTO - insert new data into a database
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

12. SQL Query Basic form: (plus many more bells and whistles)
SELECT <attributes>
FROM <one or more relations>
WHERE <conditions>

13. Simple SQL Query SELECT * FROM Product WHERE category=‘Gadgets’
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
SELECT * FROM Product WHERE category=‘Gadgets’
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99

14. Simple SQL Query
Product
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
SELECT PName, Price, Manufacturer FROM Product WHERE Price > 100
PName
Price
Manufacturer
SingleTouch
$149.99
Canon
MultiTouch
$203.99
Hitachi

15. Notation
Input Schema
Product(PName, Price, Category, Manfacturer)
SELECT PName, Price, Manufacturer FROM Product WHERE Price > 100
Answer(PName, Price, Manfacturer)
Output Schema

16. Eliminating Duplicates
Category
Gadgets
Photography
Household
SELECT DISTINCT category
FROM Product
Compare to:
Category
Gadgets
Photography
Household
SELECT category
FROM Product

17. Ordering the Results SELECT pname, price, manufacturer FROM Product
WHERE price > 100
ORDER BY pname
Ordering is ascending, unless you specify the DESC keyword.

18. And Product (pname, price, category, manufacturer)
Company (cname, stockPrice, country)
Find all products under $200 manufactured in Japan; return their names and prices.
SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country=‘Japan’ AND Price <= 200

19. And
Product
Company
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
Cname
StockPrice
Country
GizmoWorks 25
USA
Canon 65
Japan
Hitachi 15
SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country=‘Japan’ AND Price <= 200
PName
Price
SingleTouch
$149.99

20. Aggregation SELECT avg(price) FROM Product WHERE maker=“Toyota”
SELECT count(*)
FROM Product
WHERE year > 1995
SQL supports several aggregation operations:
sum, count, min, max, avg
Except count, all aggregations apply to a single attribute

21. Aggregation: Count
COUNT applies to duplicates, unless otherwise stated:
same as Count(*)
SELECT Count(category)
FROM Product
WHERE year > 1995
We probably want:
SELECT Count(DISTINCT category)
FROM Product
WHERE year > 1995

22. Simple Aggregations Purchase Product Date Price Quantity Bagel 10/21 120
Banana
10/3
0.5 10
10/10
10/25
1.50
SELECT Sum(price * quantity)
FROM Purchase
WHERE product = ‘bagel’
50 (= 20+30)

23. Grouping and Aggregation
Purchase(product, date, price, quantity)
Find total sales after 10/1/2005 per product.
SELECT product, Sum(price*quantity) AS TotalSales
FROM Purchase
WHERE date > ‘10/1/2005’
GROUP BY product

24. 1&2. FROM-WHERE-GROUPBY Product Date Price Quantity Bagel 10/21 1 20
10/25
1.50
Banana
10/3
0.5 10
10/10

25. 3. SELECT Product TotalSales Bagel 50 Banana 15
Date
Price
Quantity
Bagel
10/21 1 20
10/25
1.50
Banana
10/3
0.5 10
10/10
SELECT product, Sum(price*quantity) AS TotalSales
FROM Purchase
WHERE date > ‘10/1/2005’
GROUP BY product

26. HAVING Clause
Same query, except that we consider only products that had
at least 100 buyers.
SELECT product, Sum(price * quantity)
FROM Purchase
WHERE date > ‘10/1/2005’
GROUP BY product
HAVING Sum(quantity) > 30
HAVING clause contains conditions on aggregates.

27. NULLS in SQL Whenever we don’t have a value, we can put a NULL
Can mean many things: Value does not exists; Value exists but is unknown; Value not applicable, etc
The schema specifies for each attribute if can be null (nullable attribute) or not
SELECT PName, Price, Category
FROM Product
WHERE Category IS NULL