Temibase is an intelligent temporal database management system which has been developed by integrating Knowledge Engineering techniques with temporal relational database management systems and this system has a special subsystem to perform temporal reasoning. The main difference between commercial database systems and TEMIBASE is its ability to perform temporal data management and temporal reasoning. In this paper, we explain the query language ETSQL (Extended Temporal Structured Query Language) which has been designed for querying. TEMIBASE. ETSQL has been developed by extending the commercial query language SQL in which interval and instant operations are provided as extension. Moreover, this language provides special constructs for invoking the temporal reasoning tasks forecasting, explanation, planning and learning new rules.