With the emergence of high data rate sensor net-work applications, there is an increasing demand for high-performance query services in such networks. To meet this challenge, we propose Dynamic Conflict-free Query Scheduling (DCQS), a novel scheduling technique for queries in wireless sensor networks. In contrast to earlier TDMA protocols designed for general-purpose networks and workloads, DCQS is specifically designed for query services supporting in-network data aggregation. DCQS has several important features. First, it optimizes the query performance and energy efficiency by exploiting the temporal properties and precedence constraints introduced by data aggregation. Second, it can efficiently adapt to dynamic workloads and rate changes without explicitly reconstructing the transmission schedule. In addition, we provide an analytical capacity bound for DCQS in terms of query completion rate. This bound enables DCQS to handle overload through rate control. NS2 simulation results demonstrate that DCQS significantly outperforms a representative TDMA protocol (DRAND) and the 802.11 protocol in terms of query latency, throughput, and energy efficiency.