CREATE TABLE IF NOT EXISTS file_versions (
  id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  item_id BIGINT UNSIGNED NOT NULL,
  owner_id BIGINT UNSIGNED NOT NULL,
  version_number INT UNSIGNED NOT NULL,
  original_name VARCHAR(190) NOT NULL,
  stored_name VARCHAR(255) NOT NULL,
  extension VARCHAR(20) NULL,
  mime_type VARCHAR(150) NOT NULL,
  size_bytes BIGINT UNSIGNED NOT NULL DEFAULT 0,
  checksum CHAR(64) NULL,
  created_at DATETIME NOT NULL,
  CONSTRAINT fk_file_versions_item FOREIGN KEY(item_id) REFERENCES drive_items(id) ON DELETE CASCADE,
  CONSTRAINT fk_file_versions_owner FOREIGN KEY(owner_id) REFERENCES users(id) ON DELETE CASCADE,
  UNIQUE KEY uq_file_version_number(item_id,version_number),
  INDEX idx_file_versions_item_created(item_id,created_at),
  INDEX idx_file_versions_owner(owner_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;