Basic knowledge of PHP and database for beginners

PHP is a widely used server-side scripting language used for dynamic website development. Its combination with database systems enables more powerful applications. This article will introduce the basics of PHP and databases, including how to use PHP to connect to a database, read and write to the database, and how to protect data from security threats.

1. Connection between PHP and database

Before using PHP to connect to the database, you need to ensure the following conditions:

1. The PHP installation package contains the required Database driver;
2. The database server is already running, and the corresponding user name and password have been set;

Before connecting to the database, you need to use PHP's built-in function mysqli_connect( ) or PDO class to create a connection. These functions require the following parameters:

1. The host name of the database server;
2. Username;
3. Password;
4. The name of the database to connect to ( If not specified, the mysql database is used by default).

For example, the following code demonstrates how to use the mysqli_connect() function to connect to a mysql database:

<?php
$host = "localhost";
$username = "root";
$password = "password";
$database = "example_db";

// 创建连接
$conn = mysqli_connect($host, $username, $password, $database);

// 检查连接是否成功
if (!$conn) {
    die("连接失败: " . mysqli_connect_error());
}
echo "连接成功";
?>

2. Read the database

After connecting to the database , you can use PHP query statements to obtain data in the database. For MySQL database, you can use the SELECT statement to query data.

For example, the following code demonstrates how to use the SELECT statement to query data in a mysql database:

<?php
$sql = "SELECT id, name, email FROM users";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    while ($row = mysqli_fetch_assoc($result)) {
        echo "id: " . $row["id"] . " - Name: " . $row["name"] . " - Email: " . $row["email"] . "<br>";
    }
} else {
    echo "0 结果";
}

mysqli_close($conn);
?>

In this example, the query retrieves the user's id, name, and email columns from the database. Within the loop, use the mysqli_fetch_assoc() function to fetch the data for each row and print them to the screen.

3. Write to the database

Use the INSERT statement to insert data into the database. For example, the following code demonstrates how to use the INSERT statement to add a new user to the users table of the database:

<?php
$name = "John";
$email = "john@example.com";

$sql = "INSERT INTO users (name, email) VALUES ('$name', '$email')";

if (mysqli_query($conn, $sql)) {
    echo "新记录插入成功";
} else {
    echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}

mysqli_close($conn);
?>

In this example, the name and email are inserted into the database using the INSERT statement. The mysqli_query() function is used to execute SQL queries. If the query is successful, a "New record inserted successfully" message will be printed.

4. Protect Data

As with all web applications, protecting data from security threats is critical. Here are some best practices for protecting data in PHP and database applications:

1. Avoid using dynamic SQL statements.

Dynamic SQL statements are the most vulnerable to SQL injection attacks. Therefore, try to use parameterized queries and stored procedures, and prevent SQL injection attacks.

2. Use accurate permissions.

Ensure that database users can only access and modify the data they need to process. Changing database user permissions will help prevent bad practices and potential security breaches.

3. Encrypt sensitive data.

It is necessary to force encryption of sensitive data. You can use SSL/TLS for encryption of data transmission, or to encrypt sensitive database fields such as passwords.

Conclusion

This article introduces how to use PHP to connect to the database, read and write data, and how to protect data security. The integration of PHP and database can realize powerful applications, but it also needs to ensure the security of data. Mastering these basics will help you develop more complete and secure applications.

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