To achieve consistent results for the types of queries discussed in this section, you can either add a clause to enforce a final sort or you can run the queries in serial mode. The query clauses that provide a final sort are:
order by
distinct, except for uses of distinct within an aggregate, such as avg(distinct price)
union, but not union all
To run queries in serial mode, you can:
Use set parallel_degree 1 to limit the session to serial operation
Include the (parallel 1) clause after each table listed in the from clause of the query
