mysql限制字段值

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    status ENUM('active', 'inactive', 'pending') NOT NULL
);

CREATE TABLE products (
    id INT AUTO_INCREMENT PRIMARY KEY,
    price DECIMAL(10, 2) NOT NULL,
    CHECK (price >= 0)
);

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    email VARCHAR(255) NOT NULL UNIQUE
);

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

$conn = new mysqli($servername, $username, $password, $dbname);

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

$stmt = $conn->prepare("INSERT INTO users (username, email) VALUES (?, ?)");
$stmt->bind_param("ss", $username, $email);

$username = "john_doe";
$email = "john@example.com";

$stmt->execute();

$stmt->close();
$conn->close();
?>