When is a row added to DBA_HIST_SQLSTAT?

I don't understand the criteria that entails an additional record in the dba_hist_sqlstat view. I have expected there to be at most one entry per sql_id and snap_id, that is, the following statement to return no record: select count(*), snap_id, sql_id from dba_hist_sqlstat group by snap_id, sql_id having count(*) > 1 order by count(*) desc; *Yet*, it returns many records, indicating that it is not possible, but the normality, that the same sql statement is captured multiple times per snap_id. Additionaly, with more than one record per sql and snap period, how do I interpret the *delta* columns within this view? The documentation reads: > The delta value is the value of the statistics from the BEGIN_INTERVAL_TIME to the END_INTERVAL_TIME in the DBA_HIST_SNAPSHOT view. This doesn't really make sense to me. **Update** as per *Justin's* comment: this is not in a RAC environment: so even if I group by snap_id, sql_id, dbid, instance_number, the query returns multiple records per snap_id and sql_id.