Hi, Min, In a bitmap index, each bit of a bitmap corresponds to a particular row. Typically, the 1st bit corresponds to the 1st row, the 2nd bit corresponds to the 2nd row, and so on. In resolve a query condition such as "col4 < 1.5", a bitmap is produce to represent the answer. For example, if the 1st row and the 4th row of you data satisfy this condition, then the 1st bit of the answer and the 4th bit of the answer are set to 1, while the other bits are set to 0. Based on this answer, we can retrieve the values of col1, col2, and col3 from the 1st row and the 4th row.
Take the Java API as an example, one specify the where clause by calling build_query, which resolves the query condition and produces a bitmap to store the answer. To retrieve the rows qualify the query, one invokes the function get_qualified_ints and friends. In this case, the bitmap is not exposed to the client code. Hope this helps. John On 11/1/2009 5:19 PM, Min Zhou wrote: > Hi John, > > I guess I might not express clearly what I meant. Take a query like below: > select col1, col2, col3 from tbl where col4 < 1.5 > > how does fastbit find the records for col1, col2, col3 where col4 is > less than 1.5? > > Thanks, > Min > _______________________________________________ FastBit-users mailing list [email protected] https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users
