PHP MySQL - Stilson.net

www.it-ebooks.infoCHAPTER 30 • USING PHP WITH MYSQL// Select the database$mysqli->select_db('corporate');Once a database has been successfully selected, you can then execute database queries against it.Executing queries, such as selecting, inserting, updating, and deleting information with the mysqliextension, is covered in later sections.Once a script finishes execution, any open database connections are automatically closed and theresources are recuperated. However, it’s possible that a page requires several database connectionsthroughout the course of execution, each of which should be closed as appropriate. Even in the casewhere a single connection is used, it’s nonetheless good practice to close it at the conclusion of thescript. In any case, close() is responsible for closing the connection. An example follows:$mysqli = new mysqli();$mysqli->connect('localhost', 'catalog_user', 'secret', 'corporate');// Interact with the database…// close the connection$mysqli->close()Handling Connection ErrorsOf course, if you’re unable to connect to the MySQL database, then little else on the page is going tohappen as planned. Therefore, you should be careful to monitor connection errors and reactaccordingly. The mysqli extension includes a few features that can be used to capture error messages, oralternatively you can use exceptions (as introduced in Chapter 8). For example, you can use themysqli_connect_errno() and mysqli_connect_error() methods to diagnose and display informationabout a MySQL connection error.Retrieving Error InformationDevelopers always strive toward that nirvana known as bug-free code. In all but the most trivial ofprojects, however, such yearnings are almost always left unsatisfied. Therefore, properly detecting errorsand returning useful information to the user is a vital component of efficient software development. Thissection introduces two functions that are useful for deciphering and communicating MySQL errors.Retrieving Error CodesError numbers are often used in lieu of a natural-language message to ease software internationalizationefforts and allow for customization of error messages. The errno() method returns the error codegenerated from the execution of the last MySQL function or 0 if no error occurred. Its prototype follows:class mysqli {int errno}An example follows:591