The mysqli_multi_query() function in PHP allows you to execute multiple SQL statements in a single function call using the MySQLi extension. This is especially useful when performing a series of related queries, like inserting multiple rows or executing a combination of SELECT, INSERT, UPDATE, or DELETE statements.

🔹 Syntax:

bool mysqli_multi_query(mysqli $link, string $query)

• $link: The MySQLi connection object.
• $query: A string containing one or more SQL statements separated by semicolons (;).
• Returns true on success, or false on failure.

✅ Example 1: Multiple INSERT Statements

<?php
$mysqli = new mysqli("localhost", "root", "", "testdb");

if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

$sql = "INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');";
$sql .= "INSERT INTO users (name, email) VALUES ('Bob', 'bob@example.com');";
$sql .= "INSERT INTO users (name, email) VALUES ('Charlie', 'charlie@example.com');";

if ($mysqli->multi_query($sql)) {
    echo "Multiple records inserted successfully.";
} else {
    echo "Error: " . $mysqli->error;
}

$mysqli->close();
?>

✅ Example 2: SELECT Followed by Another Query

<?php
$mysqli = new mysqli("localhost", "root", "", "testdb");

if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

$sql = "SELECT * FROM users;";
$sql .= "SELECT * FROM orders;";

if ($mysqli->multi_query($sql)) {
    do {
        if ($result = $mysqli->store_result()) {
            while ($row = $result->fetch_assoc()) {
                print_r($row);
            }
            $result->free();
        }
    } while ($mysqli->more_results() && $mysqli->next_result());
} else {
    echo "Error: " . $mysqli->error;
}

$mysqli->close();
?>

⚠️ Notes:

• Always check for SQL injection when using dynamic queries.
• Use mysqli->store_result() to retrieve results.
• Use mysqli->next_result() to move to the next result set.
• Avoid in user-facing apps unless you're validating and sanitizing all inputs properly.