Terminology Data Types SQL Queries PHPMySQL Examples

8/8/2019 Terminology Data Types SQL Queries PHPMySQL Examples

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Database Intro

Terminology

Data Types

SQL queries

PHP/MySQL

Examples


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Database Intro (MySQL/PHP) 2

Relational Databases

Formal (mathematical) basis

Stores "relationships" by storing commonvalues in more than one table.

Not the only kind of database

object databases

hierarchical

network


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Tables

Each database is made up of one or moretables.

tables have names, typically a word that describes

what information is held in the table. A table is defined by a list of the value names/types

that compose each record held in the table.

Each name/type is called a column.

Each record is called a row.


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Example Tablewith Three Records

LastName FirstName DateOfBirth Username Password

Smith Joe 1909-03-22 joes niners

Jones Sally 1956-1-14 joness elvis

Potter Harold 1990-3-4 harry muggle

columns

rows (records)


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Possible Schema

Table People

LastName:varchar(30)

FirstName:varchar(30)

DateOfBirth: date

Username:varchar(20)

Password:varchar(10)


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Data Types Varies (a little) from one vendor to another...

Numeric Types

Integer various sizes: Small/Tiny/Medium...

Floating point various sizes: Float, Double, ...

String Types

varchar: variable length strings (up to some max)

char: fixed length strings.

and others... A number of Date/Time data types


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Column (field) names

Some people like to prefix all field names withsomething related to the table name:

Table People

pLastName:varchar(30)

pFirstName:varchar(30)

pDateOfBirth: date

pUsername:varchar(20)

pPassword:varchar(10)


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phpMySql


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Field Attributes

Is it legalfor there to be a record where a fieldis empty (NULL) ?

Number attributes:

signed vs. unsigned

autoincrement (every record gets a unique number)

Default values

Collation: for strings, what alphabetic ordering is used when

comparing strings?


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Keys and Indexes

The Database system build indexes based onthe value of certain fields (called keys).

this speeds up the process of looking for records

based on the value of the field. Every table needs aprimary key

a field whose value will be unique among allrecords.

You can specify the primary key, or let MySqldo it for you (sometimes as a combination ofmultiple fields).


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SQL

Structured Query Language

An english-like language used to expressdatabase operations.

the database system understands SQL

the application sends commands to the databaseas strings containing SQL.

in some environments this is actually hidden from theprogrammer libraries generate the SQL automatically.


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SQL in use

LocalApplication

Database

Server(process)

SQL

RemoteApplication SQL


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Some of the basic SQL commands

SELECT - lookup data.

INSERT create a new record.

UPDATE change existing records.

DELETE remove some records.

There are lots more commands, but theseprovide what we need.


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The SELECT command SELECT is used to extract data from a table

(possibly multiple tables). We have to specify:

which table(s)

what part of each record we want (what fields) We can specify:

what subset of records we want (what rows).

how to order the results limit on how many records can be returned.

lots of other options


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Simple SELECT

SELECT FirstName, LastName FROMPeople

what columns (fields) wewant from each record

The name of the table

SQL keywords


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Initial table


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Entering an SQL Query


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Another SELECT

SELECT * FROMpeopleWHERE FirstName='Joe'

* means "all columns" Indicates which records

(rows) we want.

SQL keyword


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Another Query (using a function)


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Exercise: Get dbintro Database

Grab the file labeled "dbintro sample database"(on the course home page) and save on yourcomputer.

Start up your MySQL client (phpMyAdmin orwhatever you are using).

The file contains SQL commands to create adatabase named dbinfo with tabled people andproduct tell your database to process theseSQL commands.


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dbintro Tables

PrimaryKeys


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Simple SQL Exercises

get the first names of all people

get the names and product Ids of all productswhose price is less than $1.00

T lli th d t b h t d


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Telling the database how to orderthe results.

You can add "ORDER BY" condition to the endof the query:

SELECT * FROM people ORDER BY LastName

SELECT Name FROM products ORDER BY Price DESC

SELECT * FROM people ORDER BY DateOfBirth ASC

Descending

Ascending


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Shopping Cart

Suppose we want to store a user's shoppingcart in the database.

we need some way to store this information.

we need to be careful how we set this up, doing itthe wrong way will make the system difficult tomaintain.

Requirements:

need to store information on the number of eachproduct in each users shopping cart.


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One Bad Idea

We could consider this: for each person record, add the following fields:

Snickers: integer

Candy Corn: integer Wax Lips: integer

Bubble Gum: integer

Exercise: why is this a bad idea?


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Problems

What if we add new products? M&Ms are always a good idea.

What if we remove products? The margin on Bubble Gum is too small to make $.


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Another Bad Idea

We could add a field in each product record foreach user.

obviously a waste of space.

we hope we get new users!

In general we need a solution that does notrequire changes to our database schema everytime we change our products.


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The Relationalin Relation Database

We want to establish a relationship betweenusers and products.

how many of product x is associated with user y.

We create a new table to represent thisrelationship.

needs to refer to a user.

needs to refer to a product.

we also need a quantity (of the product in theshopping cart).


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New Table: cartentries

Table cartentries

userid: integer

productid: integer

quantity: integer

Why not use FirstName,LastName and

ProductName ?what if these change? Does it invalidate some

shopping cart entries?


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A Picture of the relationship


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Exercise: Create cartentries Table

You can do this via the User Interface, or issuethe following SQL statement:

CREATE TABLE `cartentries` (`userid` INT NOT NULL ,`productid` INT NOT NULL ,`quantity` INT NOT NULL

) TYPE = MYISAM ;


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Add some records

Joe Smith (userid=1) has 3 Candy Corns (productid=2) Sally Jones (userid=2) has 1 Candy Corn

...

INSERT INTO `cartentries` VALUES (1, 2, 3);INSERT INTO `cartentries` VALUES (2, 2, 1);INSERT INTO `cartentries` VALUES (1, 4, 2);INSERT INTO `cartentries` VALUES (4, 3, 17);

All shopping cart entries


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All shopping cart entries


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A Join

You can select information from two tables,using a relationship (common field value) tojointhe tables together.

The result can contain fields from both tables. The result is still a list of records (rows)

each row contains fields from more than one table.

For example, we would like to see a list of allproducts in all shopping carts, but we want tosee product names (not ids).


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Joiningproducts and cartentries

SELECT * FROM cartentries,products WHEREcartentries.productid=products.productid

--or--

SELECT *

FROM cartentries JOIN products ON

( cartentries.productid =products.productid )


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Join result


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SQL Exercises

A query that retrieves all the informationneeded to display a user's shopping cart:

need list of products:

product name quantity

price

We need this for a single user (use userid 2).

F i ff


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Fancier stuff

SQL SELECT commands can actually do lotsmore than just retrieve data:

can compute things, like the total cost for each item inthe cart: quantity * price:

SELECT *,

cartentries.quantity * products.price AS itemtotal

FROM cartentries, products

WHERE cartentries.productid = products.productidAND cartentries.userid =1

LIMIT 0 , 30

PHP d M SQL


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PHP and MySQL

To make use of the database with PHP, weneed to do the following:

establish a connection

identify the database we want to use there can be many databases

Issue SQL commands (queries)

Retrieve and process results often display as HTML

PHP/M SQL


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PHP/MySQL

Your installation of PHP needs to have MySQLsupport (either built-in or as a module). Youtested this in HW1.

Although we can connect to any MySQL server,we will use the one running on the samemachine as the web server (your laptop).

everyone has their own database.

E t bli hi C ti


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Establishing a Connection

You need a username and password to accessyour MySQL server.

You need to know what machine the server is

running on. You call the php functionmysql_connect():

mysql_connect(server,username,password);

The function returns a PHP resource that is used by otherfunctions later, or FALSE if the connection fails.

S l C ti


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Sample Connection

// establish a connection with the MySQL server

// server is 'localhost'

// user, pass is 'joe', 'abc'

$link = mysql_connect('localhost','joe','abc');

if (! $link) {

echo ("Error" . mysql_error()."\n");

exit;

}

S l ti D t b


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Selecting a Database

Typically an application deals with a singledatabase (your MySQL server can have manydatabases).

You have to tell the server what database youare using:

mysql_select_db( databasename );

This function returns a boolean indicatingsuccess or failure.

Example: Selecting a Database


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Example: Selecting a Database

if (mysql_select_db("dbintro")) {

echo "Connected !\n";

} else {echo "Error connecting: " . mysql_error();

exit;

}

Sending a Query


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Sending a Query

The query (SQL command) is a string. we often need to build these strings based partially

on information from the HTTP request.

mysql_query(SQLstring)

returns a PHP resource (that we can use laterto get at the results) or FALSE on error.

For some kinds of SQL commands, returns TRUEor FALSE

Query Example


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Query Example

// get all people records$res = mysql_query("SELECT * FROM people");

if (! $res) {

echo "

Error: ". mysql_error() . "
\n";exit;
}

Getting the results


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Getting the results The return value from mysql_query can be

used to retrieve the results. There are many different PHP functions that can be

used to get individual records/fields.

We will look at the simplest function :

mysql_result( resource , row , fieldname );

resource is the return value from mysql_query

rowis a number (the record number in the result) fieldname is a string the identifies the field.

How many records (rows)?


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How many records (rows)?

mysql_num_rows(resource)

Example:

$res = mysql_query($q);

$num = mysql_num_rows($res);

echo "

I found $num records
";
Example Code


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Example Code

$res = mysql_query("SELECT * FROM people");if (! $res){

echo "Error!"; exit;

}

echo "All people found:\n";

$num = mysql_num_rows($res);

for ($i=0;$i

Terminology Data Types SQL Queries PHPMySQL Examples

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