CREATE TABLE audit_log (
    id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT,
    action VARCHAR(50) NOT NULL,
    table_name VARCHAR(100) NOT NULL,
    record_id INT NOT NULL,
    old_value JSON,
    new_value JSON,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE SET NULL,
    INDEX idx_user_id (user_id),
    INDEX idx_action (action),
    INDEX idx_table_name (table_name),
    INDEX idx_record_id (record_id),
    INDEX idx_created_at (created_at)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;