How do you handle data storage and retrieval in PHP web applications?

In PHP web applications, data storage and retrieval are typically handled using a database management system (DBMS). PHP can interact with a variety of DBMSs, including MySQL, PostgreSQL, Oracle, and Microsoft SQL Server, using the PHP Data Objects (PDO) extension or the MySQLi extension.

Here are the general steps for handling data storage and retrieval in PHP web applications:

1. Connect to the database: The first step is to establish a connection to the database using the appropriate credentials, such as the host name, username, password, and database name.
2. Write SQL queries: SQL queries are used to interact with the database, such as selecting, inserting, updating, or deleting data. SQL queries can be written directly in PHP or through a database abstraction layer such as Doctrine or Laravel’s Eloquent ORM.
3. Execute the queries: Once the SQL queries are written, they can be executed using the appropriate PHP functions such as PDO’s query() or prepare() and execute().
4. Fetch and process the results: After executing the SQL queries, the results are returned by the DBMS. The results can be fetched using PHP functions such as fetch(), fetchAll(), or fetchColumn(), and then processed as needed.
5. Close the database connection: Once the database interaction is complete, the connection to the database should be closed to prevent resource leaks.

In addition to using a DBMS, PHP can also interact with other types of data storage such as files, cookies, and sessions. However, databases are the most common and efficient way to store and retrieve data in PHP web applications.