Add the autoincrement
keyword after `id` int NOT NULL
:
public static function activate() {
global $wpdb;
$sql = "CREATE TABLE `{$wpdb->base_prefix}employee` (
`id` int NOT NULL autoincrement,
`name` varchar(255) NOT NULL,
`dob` date NOT NULL,
`gender` int NOT NULL,
`email` varchar(255) NOT NULL,
`joining_date` date NOT NULL,
`address` varchar(255) NOT NULL,
`salary_package` int NOT NULL,
`marital_status` int NOT NULL,
`department` varchar(255) NOT NULL,
`designation` varchar(255) NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci AUTO_INCREMENT=1;
COMMIT;";
require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
dbDelta($sql);
}