Software-Defined Networking (SDN) is revolutionizing data center networks for cloud computing with its ability to enable network virtualization and powerful network resource management that are crucial in any multi-tenant environment. In order to support sophisticated network control logic, the data plane of a switch should have a flexible Flow Table Pipeline (FTP). However, the FTP on state-of-the-art SDN switches is hardware-defined, which greatly limits the advantages of using FTP in cloud computing systems. This paper removes this limitation by introducing software-defined FTP (SDFTP), which provides an extremely flexible FTP as the southbound interface of the SDN control plane. SDFTP offers arbitrary number of pipeline stages and adaptive flow table sizing at runtime by building Software-Defined Flow Tables (SDFTs). Our analysis shows that SDFTP could create 138 times more adaptively sized pipeline stages than the hardware-defined data plane while maintaining comparable performance.