PHP-MySQL tutorial -basics

Draft

Introduction

This is a beginners tutorial for PHP and MySQL. Is is made from (older 10 year old) slides and needs some extra work ... - Daniel K. Schneider

Objectives

• Understand the "traditional" low-level PHP-MySQL interface
• Learn how to connect to a MySQL database and send SQL commands
• Understand how to extract information from the results

Prerequisites

• Some PHP
• SQL and MySQL tutorial
• Some HTML, e.g. read the HTML and XHTML elements and attributes tutorial

Next steps

• PHP - MySQL - XML tutorial - basics (create XML as result of db queries and render it with XSLT)
• XQuery tutorial - basics (if you have interest in XML databases)

PHP and MYSQL

PHP can interact with most RDBMS.

To interact with MySQL a PHP 5.2+ developer has three options. Let's shortly have a look them.

(1) PHP's MySQL Extension is the "traditional API" and works with all MySQL version in use (as of Jan 2010). “This is the original extension designed to allow you to develop PHP applications that interact with a MySQL database. The mysql extension provides a procedural interface and is intended for use only with MySQL versions older than 4.1.3. This extension can be used with versions of MySQL 4.1.3 or newer, but not all of the latest MySQL server features will be available.”(Overview, PHP Manual, retrieved 18:58, 6 February 2010 (UTC)) However, as of early 2010, it seems to us, that most CMS still use this older interface, probably in order to support older PHP/MySQL installations...

(2) PHP's mysqli Extension adds extra functionalities. “The mysqli extension, or as it is sometimes known, the MySQL improved extension, was developed to take advantage of new features found in MySQL systems versions 4.1.3 and newer. The mysqli extension is included with PHP versions 5 and later. The mysqli extension has a number of benefits, the key enhancements over the mysql extension being: Object-oriented interface [(but also a procedural one)], Support for Prepared Statements, Support for Multiple Statements, Support for Transactions, Enhanced debugging capabilities, Embedded server support.”(Overview, PHP Manual, retrieved 18:58, 6 February 2010 (UTC))

(3) The PHP Data Objects (PDO) is an abstraction layer. “PHP Data Objects, or PDO, is a database abstraction layer specifically for PHP applications. PDO provides a consistent API for your PHP application regardless of the type of database server your application will connect to. In theory, if you are using the PDO API, you could switch the database server you used, from say Firebird to MySQL, and only need to make minor changes to your PHP code. [...] While PDO has its advantages, such as a clean, simple, portable API, its main disadvantage is that it doesn't allow you to use all of the advanced features that are available in the latest versions of MySQL server. For example, PDO does not allow you to use MySQL's support for Multiple Statements.” (Overview, PHP Manual, retrieved 18:58, 6 February 2010 (UTC)) Alternatively, many 2rd party abstraction layers exist.

The principle shortly :

• In PHP, SQL queries are built (ususally as a result of user request)
• These queries are sent by PHP to a MySQL server
• MySQL returns a result datastructure
• Thes results from MySQL are then arranged an inserted into an HTML page.

The MySQL extension

A complete documented example:

• application

(Sorry, the application itself is currently locked since we can't cope with spamming ...)

To show all records: dump_results.phps

To add records we need two scripts:

new-entry.php produces the HTML form

insert-entry.php inserts the values from the forms an gives some feedback.

Add a record (new-entry.phps and insert-entry.phps)

Same principle for editing:

edit-entry.php produces the form

replace-entry.php replaces old values by new ones.

Edit a record (edit-entry.phps and replace-entry.phps)

Kill a record (delete-entry.phps)

Connecting to a database

When interfacing a PHP script to a database, you first have to connect to a server and then select the database. Connecting to a database is fairly easy.

Information you need:

1. the host name of the database (usually "localhost", meaning that the MySQL server sits on the same machine as your web server)
2. the database user name and password

Syntax for a persistent connection:

mysql_pconnect(host, username, password);

Example:

$link = mysql_pconnect("localhost","clavel","secret");

$link is a so-called link identifier and will contain the link to the open connection (or "FALSE" if something went wrong).

Then you need some code for selecting a specific database. Since a MySQL server hosts several databases, you need to tell which one you will use.

Syntax:

 mysql_select_db(dbname, [linkID]);

Example:

mysql_select_db("demo");

Sending a SQL statement

Once you are connected to a database through a MySQL server, you can send SQL statements using the mysql_query function. This call will return a resource identifier that points to a result. The PHP manual defines a resource as “a special variable, holding a reference to an external resource. Resources are created and used by special functions.” In the case of MysQL, the resource is some kind of table that includes columns and rows. As we shall see below, you then have the choice of a series of special functions to retrieve data from it.

Example:

$result = mysql_query("SELECT * FROM demo1");

$result is a so-called resource, i.e. a special variable, holding a reference to an external resource. It can be used like a "boolean" to test if a result was found.

A resource (TRUE) if ok

0 (FALSE) if there was a problem.

Processing of results

There exist several ways of dealing with the result. We first will show how to deal with the results "row by row" using mysql_fetch_row():

Syntax:

mysql_fetch_row(resource)

SQL/result example:

 $result = mysql_query("SELECT * FROM demo1")
 $row = mysql_fetch_row ($result);

Mysql_fetch_row returns a line of the result as an array (a list of values). If you call it again, it will return the next line

Number of fields returned:

 mysql_num_fields

Example:

mysql_num_fields(resource)
$nb_champs = mysql_num_fields($result);

Dealing with errors

The minimal precautions you should take is make sure that data base connection and the SQL query went ok, else you should abort execution of the script. The PHP die() function will exactly do this.

$DB_link = mysql_connect($host, $user, $pass) or die ("Could not connect to host.");
mysql_select_db($database, $DB_link) or die ("Could not find or access the database.");
$result = mysql_query ($SQL_query, $DB_link) or die ("Data not found. Your SQL query didn't work... ");

For most mysql operations, there can be errors and PHP allows to display error messages generated by the MySQL server. You can use the following PHP functions to display more information.

mysql_errno(resource)

returns a number code for the last mySQL operation or zero (0) if not error was found.

mysql_error(resource)

returns an string with some extra information.

Here is simple error handling example

<?php
// next line is correct
$link = mysql_connect("localhost", "mysql_user", "good_password");

// next line includes a bad database name
if (!mysql_select_db("nonexistentdb", $link)) {
    echo mysql_errno($link) . ": " . mysql_error($link). "\n";
}

// next line is correct
mysql_select_db("good_db", $link);

// next line includes a bad table name
if (!mysql_query("SELECT * FROM nonexistenttable", $link)) {
    echo mysql_errno($link) . ": " . mysql_error($link) . "\n";
}
?>

For the two errors you would see something like this:

1049: Unknown database 'nonexistentdb'
1146: Table 'good_db.nonexistenttable' doesn't exist

Remark: You also can test SQL expressions with a database administration tool.

Generation of an HTML table with the results

(Locked) life example: dump_results_demo.php

Source code:

dump_results_demo.phps

 <?php
 mysql_pconnect("localhost","nobody","");
 mysql_select_db("demo");
 $result = mysql_query("SELECT * FROM demo1");
 ?>
 <table  border="1">   <tr>
 <?php
 while  ($row  =  mysql_fetch_row($result))  { 
     echo  "<tr>"; 
     for  ($i=0;  $i<mysql_num_fields($result);  $i++)  { 
       echo  "<td>"; 
       // test if this is the URL
       if ($i == 4) { echo  "<a href='$row[$i]'>$row[$i]</a>";  }
       else {  echo  "$row[$i]"; }
       echo  "</td>"; 
     } }
 ?>
 </table>

Processing a result using field names with mysql_num_rows ()

Syntax:

 mysql_num_rows(resource);

Example:

$nb_enregistrements = mysql_num_rows($result);

Returns number of returned records in $result

The mysql_result() function allows to retrieve cells:

 mysql_result(resource, index, champ);

Example:

$nom = mysql_result($result,0,’fullname’);

index holds the record number. Indexation starts at 0 ! (zero).

champ is the name of the field.

se next slide ...

HTML generation using field names

http://tecfa.unige.ch/guides/php/examples/mysql-demo-source/dump_results_demo2.php

dump_results_demo2.phps

dump_results_demo2.source

 <?php 
 mysql_pconnect( "localhost", "nobody", "")  or  die( "Unable  to  connect  to  SQL  server"); 
 mysql_select_db("demo")  or  die ( "Unable  to  select  database"); 
 $result  =  mysql_query( "select * from demo1"); 
 ?> 
   <table  border="1"> 
 <?php
 $i = 0;
 while ($i < '''mysql_num_rows'''($result)) {
   echo  "<tr>";   
   echo  "<td>";   
   echo '''mysql_result'''($result,$i,’id’);
   echo  "</td>";   
   echo  "<td>";   
   echo '''mysql_result'''($result,$i,’fullname’);
   echo  "</td>";   
   echo  "<td>";   
   echo '''mysql_result'''($result,$i,’love’);
   echo  "</td>";   
   echo  "<td>";   
   echo '''mysql_result'''($result,$i,’sports’);
   echo  "</td>";   
   echo  "</tr>"; 
   $i++;
 }
   echo  "</table>"; 
 ?>

Workthough example: Guestbook

Example files:

Create a comments directory in your web server.

Copy the forllowing files: comments-list.source, comments-insert.source, comments.html from:

http://tecfa.unige.ch/guides/tie/code/act-php-mysql-FC/

Rename .source to .php !!!

Structure of the comments table:

http://tecfa.unige.ch/guides/tie/code/act-php-mysql-FC/solution/comments-table.txt

 create table comments (
     id int(10) default ’0’ not null auto_increment,
     nom char(20) default ’’ not null,
     prenom char(20) default ’’,
     email char(50) default ’’ ,
     computer char(10),
     browser char(10),
     version char(10),
     comments char(200),
     primary key (id),
     key nom (nom)
 );

Task

comments.html displays the form and sends values to comments-insert.php.

comments-insert.php writes data to mySQLServer : localhost database name

.....table : comments database user name: ....database user password : ....

comments-list.php will display all comments in a table.

the HTML is funtional, but you will have to fix the 2 php files (comments are in french sorry)

Start with comments-insert.php then file comments-list.php

Solution:

http://tecfa.unige.ch/guides/tie/code/act-php-mysql-FC/solution/comments.html