PHP and MySQL

Why Use a Database  Easy access to data  Simultaneous access by multiple users is handled properly  Security - easy to control access to data

Databases  A database is a collection of data organized for efficient access  A relational database is a collection of tables  Columns represent attributes  Rows represent entities  We will use MySQL for our examples

MySQL  MySQL is a free database system which is running on onyx  Standard port for MySQL is 3306  For this class, use the user name php_user and the password web2dtbs  php_user has access to the restaurant database and all databases whose names begin with test  php_user has enough privileges to create and use any database whose name has the form test_*  Please, do not drop any databases from the system except your own.

Interacting with MySQL from the shell Starting the command-line client mysql -p -u php_user Find out what databases exist show databases \g Select a database to use use databaseName \g Show all the tables in the database show tables \g Quit \q

Creating a new database  You could do this from a PHP program  Probably easier to do it manually - you don't usually want to do it more than once  Create a set of files  Define the tables  Load initial data into the tables  The directory ~tcole/teaching/cs498/demo/db on onyx has the files used to set up the restaurant database

Using MySQL from a PHP program  PHP has a collection of add-on modules called PEAR (PHP Extension and Application Repository)  One of the modules is DB which has a set of functions for interacting with databases  You write the same PHP code for any database program  Alternately, there are separate extensions for each database program (mysql for MySQL)

Using PEAR to connect  Load the DB module require 'DB.php';  Connecting  Use the connect function with a Data Source Name argument specifying host, user, database client, database  Get back an object you can use to interact with the database $db = DB::connect(

Checking for Success  The isError method in the DB module will tell yow whether you connected successfully  DB::isError($db) returns true if there was a problem  The database object has a getMessage method which provides some information  $db->getMessage()  We can set the error handling mode $db->setErrorHandling( PEAR_ERROR_DIE);

Interacting with the database  The database object has a query method that takes an SQL command as its argument  $q = $db->query( queryString)  the method returns an object  the returned object can be tested by DB::isError( $q)

Retrieving Data  Use the SQL SELECT command in the query string to retrieve data from the database $q = $db->query( 'SELECT dish_name, price FROM dishes');  The returned object gives you access to the returned data  $row = $q->fetchRow() returns either the next row (as an array) or false if there are no more  $q->numRows() returns the number of rows  $q->getAll() returns an array containing all the rows

Inserting data  Use the SQL INSERT command in your query string $q = $db->query( "INSERT INTO dishes (dish_name, price, is_spicy) VALUES ('Sesame Seed Puff', 2.50, 0)");  There are several forms for INSERT

Inserting Data from Forms  You can use form data either to create new rows or as part of the WHERE clause in a SELECT command  To make your database safe from malicious users, use placeholders to put form data into a query string $db->query( 'INSERT INTO dishes (dish_name, price) VALUES (?, ?)', array( $_POST['new_dish_name'], $_POST['new_price']));  This form of query takes care of single quotes in the entered text

Modifying data  Use the SQL UPDATE command in your query string $q = $db->query( "UPDATE dishes SET price = price * 1.1");  There are several forms for UPDATE  generally want to use a where clause to limit which rows are updated

Removing Data  Use the SQL DELETE command in your query string $q = $db->query( "DELETE FROM dishes WHERE price < 1.00");  Without the WHERE, all rows are deleted  You can check how many rows were removed with  $db->affectedRows()

MySQL without PEAR  You can use databases without using PEAR  Commands are different for each database  Use mysql (or mysqli) for MySQL databases  Which you use depends on what versions are being used; mysql seems to work on onyx

mysql Commands  Commands $db = mysql_connect( host, user, pwd, db) $q = mysql_query($db,sql) $row = mysql_fetch_row($q) msql_affected_rows( $q) mysql_num_rows( $q)  There is no automatic error handling but you can use mysql_connect_error() to check manually

Sources  Learning PHP 5 by David Sklar  Web Database Applications with PHP and MySQL by Hugh E. Williams and David Lane  PHP home page 