The mysqli_num_rows() function in PHP is used to get the number of rows in a result set returned by a MySQL query. It is commonly used after executing a SELECT query to determine how many rows are in the result set.

Syntax:

mysqli_num_rows($result);

• $result: The result set from a MySQL query (mysqli_query()), which must be a valid result of a SELECT query.

Return Value:

• It returns the number of rows in the result set as an integer.
• If no rows are found, it returns 0.
• If the query fails or the result is not a valid resource, it returns FALSE.

Example 1: Basic Usage of mysqli_num_rows

<?php
// Create a connection
$conn = mysqli_connect("localhost", "username", "password", "database");

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

// Execute a query
$query = "SELECT * FROM users";
$result = mysqli_query($conn, $query);

// Get the number of rows
$num_rows = mysqli_num_rows($result);

// Output the number of rows
echo "Number of rows: " . $num_rows;

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

In this example:

• We connect to the database and run a SELECT * FROM users query to retrieve all the rows from the users table.
• mysqli_num_rows($result) returns the number of rows in the result set.
• The result is printed using echo.

Example 2: Checking if Data Exists

You can also use mysqli_num_rows() to check if the query returned any results:

<?php
// Create a connection
$conn = mysqli_connect("localhost", "username", "password", "database");

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

// Execute a query to find a user with a specific email
$email = 'example@example.com';
$query = "SELECT * FROM users WHERE email = '$email'";
$result = mysqli_query($conn, $query);

// Check if any row is returned
if (mysqli_num_rows($result) > 0) {
    echo "User exists!";
} else {
    echo "No user found with that email.";
}

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

Here:

• We query the users table to check if there’s a user with the specified email.
• mysqli_num_rows($result) checks if the result contains any rows. If it does, we know the user exists.

Example 3: Using mysqli_num_rows() in a Loop to Display Data

<?php
// Create a connection
$conn = mysqli_connect("localhost", "username", "password", "database");

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

// Execute a query to get all users
$query = "SELECT * FROM users";
$result = mysqli_query($conn, $query);

// Check if there are any users
if (mysqli_num_rows($result) > 0) {
    // Loop through the result and display data
    while ($row = mysqli_fetch_assoc($result)) {
        echo "Name: " . $row['name'] . "<br>";
        echo "Email: " . $row['email'] . "<br><br>";
    }
} else {
    echo "No users found.";
}

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

In this example:

• We check if the query returns any rows using mysqli_num_rows().
• If rows are returned, we loop through them using mysqli_fetch_assoc() to display each user's name and email.

Common Use Cases:

• To determine if a query returned any results.
• To validate the number of records found in a query.
• To control the flow of your program based on the number of records retrieved.

Notes:

• mysqli_num_rows() only works with SELECT queries, not with INSERT, UPDATE, or DELETE queries.
• If the result is empty, mysqli_num_rows() will return 0.