MySQL

Let’s Get Relational

Tables

• Think of each table as a spreadsheet

• We define columns, also known as fields, which classify our data

• Each record in the table is a row

Data Types

• Varchar

– Variable Characters, specify up to how many characters something will be

• Char

– A set number of characters, good for things like state abbreviations

• Int

– Whole numbers, positive or negative

Data Types

• Float

– Floating Point, also known as a decimal

• Text

– A huge blob of text, like a paragraph or more

• TinyInt / Bit / Boolean

– 0 or 1, True or False

• DateTime

– A date and time 0000-00-00 00:00:00

Data Types

• Depending on the flavor of SQL (Oracle, MySQL, MSSQL, PostgreSQL, etc) there are many more

• Don’t get overwhelmed, just think of what will be best in terms of sorting and lookups

User Table Example

• Username

– Varchar

• Password

– Varchar

• ID

– Integer

• AccountCreated

– DateTime

PHPMYADMIN

CRUD

• Create

• Retrieve

• Update

• Delete

Create

• INSERT is used to create a new record in the database

• INSERT VALUES (username, password) INTO users (‘fluffybunny’, ‘123456’)

Retrieve

• SELECT is used to retrieve a record in the database

• SELECT username, password FROM users WHERE ID = 1

Anatomy of SELECT

• SELECT [column]– The command

• FROM [table]– The table you want to select from

• WHERE *column+ = ‘value’– Specifics

• ORDER BY [column] [ASC/DESC]– Sort by column

• LIMIT [Number]– Limit the number of records returned

UPDATE

• UPDATE is used to change record(s) in the database

• UPDATE users SET username = ‘FluffyBuns’ WHERE ID = 1

DELETE

• DELETE is used to remove records from the database

• DELETE FROM users WHERE ID = 1

** if you do not specify anything in the WHERE clause, it will delete everything in that table

Users and Groups

ID User

1 John

2 Jane

3 Sally

4 Ryan

5 Joe

ID Group

1 Sharks

2 Ducks

3 Lemurs

UserID GroupID

1 2

2 2

3 1

4 1

5 3

Users Groups UserGroups

Joins

• SELECT User, Group FROM UsersJOIN UserGroups ON Users.ID = UserGroups.UserIDJOIN Groups ON UserGroups.GroupID = Groups.IDWHERE Group = ‘Sharks’

IN

• SELECT User FROM Users WHERE ID IN (1,2)

• SELECT User FROM Users WHERE ID IN (SELECT UserID FROM UserGroups WHERE GroupID = 2)

BETWEEN

• SELECT User FROM Users WHERE ID BETWEEN 3 AND 5

Conditions and Operators

• WHERE can also use wildcards for text– WHERE Column IS LIKE ‘%something%’

• WHERE can use more than =– WHERE ID < 4– WHERE ID <= 4

• WHERE can combine conditions– WHERE Column = ‘A’ AND Column2 = ‘B’– WHERE Column = ‘A’ OR Column2 = ‘B’– WHERE (Column = ‘A’ OR Column2 = B’) AND Other = ‘C’

Nerding Out

• SQL has functions, like COUNT and SUM

• SELECT Customer, SUM(Amount) FROM Orders GROUP BY Customer

• SELECT COUNT(Customer) FROM Orders GROUP BY Customer

Indexes

• It’s a good habit to create a column for each table that acts as an ID

• We can put an index on the ID and it can speed up the query time

• Unless you’re dealing with really big datasets, you probably won’t have to worry about this

Database Design

• Design a schema for a social network– I’m cool with stretching this to something else

• At a minimum it must contain:– Users

– Posts

– Friend Relationships

– Likes

• You will create a web interface for this database later