AJAX and PHP

Server-Side Techniques with PHP and MySQL
This data will be used when performing database operations. Any database operation consists of
three mandatory steps:
1. Opening the database connection
2. Executing the SQL queries and reading the results
3. Closing the database connection
It's a good practice to open the database connection as late as possible, and close it as soon as
possible, because open database connections consume server resources. The following code
snippet shows a simple PHP script that opens a connection, reads some data from the database,
and closes the connection:
// connect to the database
$mysqli = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);
// what SQL query you want executed?
$query = 'SELECT user_id, user_name FROM users';
// execute the query
$result = $mysqli->query($query);
// do something with the results...
// ...
// close the input stream
$result->close();
// close the database connection
$mysqli->close();
Note that we use the mysqli library to access MySQL. This is a newer and improved
version of the mysql library, which provides both object-oriented and procedural
interfaces to MySQL, and can access more advanced features of MySQL. If you have
older versions of MySQL or PHP that don't support mysqli, use mysql instead.
The exercise that follows doesn't contain AJAX-specific functionality; it is just a simple example
of accessing a MySQL database from PHP code.
Time for Action—Working with PHP and MySQL
1. Connect to the ajax database, and create a table named users with the following code:
CREATE TABLE users
(
user_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
user_name VARCHAR(32) NOT NULL,
PRIMARY KEY (user_id)
);
2. Execute the following INSERT T commands to populate your users table with some
sample data:
INSERT INTO users (user_name) VALUES ('bogdan');
INSERT INTO users (user_name) VALUES ('filip');
INSERT INTO users (user_name) VALUES ('mihai');
INSERT INTO users (user_name) VALUES ('emilian');
INSERT INTO users (user_name) VALUES ('paula');
INSERT INTO users (user_name) VALUES ('cristian');
Because user_id is an auto_increment column, its values will be generated by the database.
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