Software-Defined Networking (SDN) and the Internet of Things (IoT) are collaborating in a transformative way to establish connections. The Internet of Things enables remote management of equipment as well as real-time data exchange via its billions of connected devices. This is supported by SDN's provision of a comprehensive network view, which enables remote access and control for both users and operators. The growing popularity of IoT and SDN represents a paradigm change that is fundamentally altering the environment of intelligent services and interconnected devices. The profound impact that their mutual relationship has had on contemporary connectivity is concisely outlined in this review. This extensive review paper investigates the advantageous association between Software-Defined Networking (SDN) and the Internet of Things (IoT), throwing insight on their combined capability to enhance network performance. Underscoring the critical contribution of SDN to centralized threat detection across Wide Area Networks, Access Networks, and Edge Networks in the IoT domain, the study emphasizes the critical role of SDN in augmenting flexibility, manageability, and security in these networks. The advent of Software-Defined Internet of Things (SDIoT) becomes an innovative focal point, demonstrating the significant effects that it has on IoT networks. The review further explores the frequent coexistence of terms related to SDN and IoT networks, underscoring their broad range of applications. Furthermore, the paper critically examines the difficulties associated with supervising IoT networks and assesses recent strategies that have been implemented in the past five years to overcome these obstacles. These strategies include load balancing, energy management, provisioning security services, and defect tolerance. The article generally presents an in-depth view on the ways in which SDN enhances the effectiveness and protection of IoT networks. As a result, it provides policymakers, practitioners, and researchers with invaluable information.