yep...as everyone has already indicated, database tables are sets, with no pre-defined time/sequence for results, unless you implement one (using SQL order by). This allows for the notion/use of atomic updates, e.g. (SQL pseudocode) UPDATE TABLE test SET some_time_column TO now()
All the rows will be set with the same value returned by now() function. "set theory" applies to relational databases, and it breaks if values change over time.