Unlike traditional approach of entering the aggregate computation in batch mode and waiting till it is completely processed, online aggregation is the aggregates that let the user to obtain partial results and allows the user to stop the computation in between. These type of aggregates are useful in applications where an exact value is not needed and an approximate will suffice. The requirements of online aggregation and the details of an extension of POSTGRES95 to support online aggregation are discussed in [HHW97].