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Once the session has been initialized, the data that must remain persistently can be stored in the superglobal $_SESSION array. The following are examples of storing persistence data to this superglobal array: <?php $_SESSION['fname'] = 'George'; $_SESSION['lname'] = 'Burnes'; ?>

As stated earlier, the process of PHP maintaining information from one session to the next for a visitor is pretty straight forward without lacking in capability. This maintaining of information (getting to know the end user) is accomplished through session handling tasks. Starting a Session It is necessary to tell PHP when to open up its eyes and prepare for the possibility of having to get to know an end user. This process is accomplished through the function session_start(). This function initializes the session data or continues the current session that is being passed by a request, such as a GET, POST or a cookie. <?php session_start(); ?> Setting up the Session "Key" After starting the session process, it is important to identify the "key" by which the user will be remembered. This key is stored on the end users machine and is called when interacting with the end user machine with the same function; session_id(). <?php session_s

What is Session Handling Hyper Text Transfer Protocol (HTTP) is the method on which information is transferred from a server to a client on the world wide web. This protocol is static in nature, that is every request is a new request and no persistence (or memory of a previous transfer) remains within the protocol itself. This has its advantages in the form of safety, the requests by either the client or the server has no long term affects on the other. This provides a level of security that could be related to a friendly acquaintance with each other and no long term affects are felt by the interaction. However, for the application developer (and dare it be said, also for the end user), there are times when a more intimate relationship is needed to add value to the experience. This is where session handling comes in. Basically, when a user interacts with a web page, the application attempts to get to know the person and retain a memory of their visit. Maintaining State I

Even though developers (most at least) strive for an application free of bugs, no application (except minor projects) can be expected to be completely bug-free. For that purpose, a good practice for programmers is to build in code that will trap and display errors in a way that is both meaningful and useful to assist in the correction of the error. PHP offers two functions that can display error messages from MySQL: • mysql_error() - This function displays the error message (if there was one) from the last MySQL function. The language that the message will be displayed in is based on the target language that is setup in the MySQL server. However, even if a fluent speaker of the message language were to read the majority of error messages returned, they would most likely still have a difficult time understanding what was said. Needless to say, error messages from MySQL are not very verbose or informative. <?php // Load variables used in mysql_connect and connect to serv

The most complete way to retrieve metadata is by using a SELECT statement against the INFORMATION_SCHEMA database in the MySQL server. However, there are times that is overkill for the data needing to be collected for a PHP application. With that said, PHP offers multiple functions that provide methods for retrieving a small amount of metadata about the data in the MySQL server. Database Metadata The mysql_list_dbs() function retrieves the name of all the databases found on the server that are accessible by the user requesting the information: <?php // Load variables used in mysql_connect and connect to server include "connect_info.php"; $linkID1 = mysql_connect($dbhost,$dbuser,$dbpass) or die("Could not connect to MySQL server"); // Retrieve the names of the databases accessible by the user $schema_results = mysql_list_dbs($linkID1); print "The databases available to the root user are:<br>\n"; while (list($schema) = mysql_fetch

The INFORMATION_SCHEMA is a virtual database that is automatically created and populated by MySQL, there is no need to create an INFORMATION_SCHEMA database. There also is no associated file structure due to the fact that the contents of the data are actual views, rather than logical data being stored in any one location. Only SELECT statements are allowed against the tables in the INFORMATION_SCHEMA database. The following SELECT example demonstrates some of the metadata that can be viewed: <?php // Load variables used in mysql_connect and connect to server include "connect_info.php"; $linkID1 = mysql_connect($dbhost,$dbuser,$dbpass) or die("Could not connect to MySQL server"); // Execute Query to Collect Metadata $query = "SELECT TABLE_NAME, ENGINE, TABLE_ROWS, UPDATE_TIME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA='world'"; $results = mysql_query($query, $linkID1); // Build HTML Table of Results print "<table

Databases contain data, but information about the way databases are structured is metadata. The primary way of obtaining metadata is by using the INFORMATION_SCHEMA database to access metadata. MySQL produces metadata for several aspects of database structure. To name a few, metadata can be obtained from such database information as names of databases and tables, information about columns and indexes in tables, or stored routine definitions. Database Information In the world of web based applications. getting information about databases is important to be able to create generic and scalable applications. This section will demonstrate how to obtain information concerning the databases, the tables and the columns located in the MySQL server. Due to the fact that the root user is being used to log into the MySQL server, the resulting queries against the INFORMATION_SCHEMA database will result in a display of all information contained on the server. However, the majority of users