The wireless sensor network is emerging as a new hotspot by exploiting the cooperation of hundreds to thousands of cheap nodes. Data gathering and data aggregation are key issues in the network. This article has taken a deep view into the current solutions for the data gathering and data aggregation. First, it has introduced the basic concepts, i.e., the data gathering system, data structure, data aggregation function and routing protocols. Secondly, it has explored the current data gathering protocols, and accordingly introduced three important tree-based / flat routing protocols, namely, SPIN, Directed Diffusion and ELECTION-based protocol, one cluster-based hierarchical protocol named as LEACH, as well as one location-based protocol named GAF. Finally, it has concerned with the real-time requirement in the applications, and introduced a novel solution by converting the real-time requirement into two constraints: node degree bounded and tree height bounded, and provided solutions for it.