If someone out there knows a better or more common name for the problem, then please say so by leaving a comment.An example says more than a thousand words, so here is an example of what I mean by the term:Suppose I have this table:rwijk@ORA10GR2> create table mytable (code,start_date,end_date,value) 2 as 3 select 'group1', date '2007-01-01', date '2007-01-10', 11 from dual union all 4 selec