PHP is a widely used server-side scripting language and is often used to handle the development of web applications. In many cases, PHP needs to process large amounts of data through the database, and database operations in PHP are very important. This article will introduce the basic knowledge of database operations in PHP.

1. Data storage: file or database?

In PHP, data can be stored in files or in databases. So, when should you choose which option?

When the amount of data is small and does not need to be modified frequently, it may be better to use a file because it is easier to understand and process. But if the amount of data is large, or frequent updates, queries and other operations are required, it is more appropriate to use a database. This is because databases have better scalability and higher performance and can better handle large amounts of data and frequent access.

2. Connect to the database

For database operations in PHP, you first need to connect to the database. Before connecting, you need to determine the following parameters:

• Host name: usually localhost or the IP address where the database is located.
• Username: Database login name.
• Password: Database login password.
• Database name: The name of the database to connect to.

The statement to connect to the database is as follows:

$conn = mysqli_connect($servername, $username, $password, $dbname);

Among them, $servername represents the host name, $username represents the user name, $password represents the password, and $dbname represents the database name. This statement returns a connected object, or false if the connection fails.

3. Execute SQL statements

After connecting to the database, you can execute SQL statements to perform various operations, such as inserting, deleting, modifying and querying data.

In PHP, you can use the mysqli_query() function to execute SQL statements. This function requires two parameters, one is the connection object and the other is the SQL statement to be executed. For example:

$sql = "SELECT * FROM users";
$result = mysqli_query($conn, $sql);

This statement performs a query for all users and saves the results in the $result variable. If the statement is executed successfully, $result will contain the query results, otherwise false will be returned.

4. Processing query results

After executing the query statement, the results usually need to be processed. In PHP, the result can be a resource type, which needs to be converted to an array type using the mysqli_fetch_array() function.

while($row = mysqli_fetch_array($result)) {
    echo $row['username'] . "的郵箱地址是：" . $row['email'];
}

This statement will read the query results row by row and store the results in the $row array. Then print out the username and email address.

If you need to update or delete data, you can use the mysqli_query() function to perform related operations. For example, you can use the following statement to delete a user named "Tom":

$sql = "DELETE FROM users WHERE username='Tom'";
mysqli_query($conn, $sql);

It should be noted that modification or deletion operations must have corresponding permissions to perform.

5. Close the connection

After completing the database operation, the database connection must be closed. Use the mysqli_close() function to close the connection:

mysqli_close($conn);

6. Security issues

When using the database, you need to pay attention to security issues. For example, the mysqli_real_escape_string() function should be used to escape user-entered data to prevent SQL injection attacks.

$username = mysqli_real_escape_string($conn, $_POST['username']);

The above code escapes the username entered by the user and then stores it in the $username variable.

In addition, you also need to restrict access to the database in the PHP code, for example, only allow specific users to perform specific operations.

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