To perform an UPDATE query in PHP using MySQLi in procedural style, follow these steps:

1. Establish a Database Connection

First, you need to connect to the MySQL database using mysqli_connect().

$conn = mysqli_connect('localhost', 'username', 'password', 'database');

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

2. Prepare the UPDATE Query

Construct the SQL UPDATE query string. For example, if you want to update the email of a user in a table named users, your query might look like this:

$sql = "UPDATE users SET email = 'newemail@example.com' WHERE username = 'john_doe'";

3. Execute the Query

Use mysqli_query() to execute the UPDATE query.

if (mysqli_query($conn, $sql)) {
    echo "Record updated successfully";
} else {
    echo "Error updating record: " . mysqli_error($conn);
}

4. Close the Database Connection

After executing the query, close the connection using mysqli_close().

mysqli_close($conn);

Full Example

Here’s a complete example demonstrating an UPDATE query using MySQLi in procedural style:

<?php
// Step 1: Connect to the database
$conn = mysqli_connect('localhost', 'username', 'password', 'database');

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// Step 2: Prepare the UPDATE query
$sql = "UPDATE users SET email = 'newemail@example.com' WHERE username = 'john_doe'";

// Step 3: Execute the query
if (mysqli_query($conn, $sql)) {
    echo "Record updated successfully";
} else {
    echo "Error updating record: " . mysqli_error($conn);
}

// Step 4: Close the connection
mysqli_close($conn);
?>

Notes

• Error Handling: Always check if mysqli_query() returns false to handle potential errors in the query execution.
• Escaping Strings: To prevent SQL injection, especially when dealing with user input, use mysqli_real_escape_string() to escape input values before including them in your query.
• Prepared Statements: For better security and to handle dynamic data safely, consider using prepared statements with mysqli_prepare() and mysqli_stmt_bind_param(). This approach helps prevent SQL injection attacks.

Here’s an example using prepared statements for the UPDATE query:

<?php
// Step 1: Connect to the database
$conn = mysqli_connect('localhost', 'username', 'password', 'database');

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// Step 2: Prepare the UPDATE query
$stmt = mysqli_prepare($conn, "UPDATE users SET email = ? WHERE username = ?");

// Bind parameters
mysqli_stmt_bind_param($stmt, "ss", $email, $username);

// Set parameters and execute
$email = 'newemail@example.com';
$username = 'john_doe';
mysqli_stmt_execute($stmt);

if (mysqli_stmt_affected_rows($stmt) > 0) {
    echo "Record updated successfully";
} else {
    echo "No record updated or an error occurred";
}

// Close the statement and connection
mysqli_stmt_close($stmt);
mysqli_close($conn);
?>