This paper proposes an approach to querying a relational database $\mathcal{D}$ and a graph G taken together in SQL. We introduce a semantic extension of joins across $\mathcal{D}$ and G such that if a tuple t in $\mathcal{D}$ and a vertex v in G refer to the same real-world entity, then we join t and v to correlate their information and complement tuple t with additional properties of vertex v from the graph. Moreover, we extract hidden relationships between t and other entities by exploring paths from v. To support the semantic joins, we develop an extraction scheme based on LSTM, path clustering and ranking, to fetch important properties from graphs, and incrementally maintain the extracted data in response to updates. We also provide methods for implementing static joins when t is a tuple in $\mathcal{D}$, dynamic joins when t comes from the intermediate result of a sub-query, and heuristic joins to strike a balance between the complexity and accuracy. Using real-life data and queries, we experimentally verify the effectiveness, scalability and efficiency of the methods.