About ordering
1.Group By2 Order By3 Select DistINCT4.CREATE INDEX5.UNION MIUS6.MEGER JON LARGE_POOL_SIZE ALTER SESSION SET SORT_AREA_SIZE =?
Disk sort is 14,000 times slower than Memory Sort
Sort_area_retained_size reserved space to optimize Sort is not very useful
Sort_multiblock_read_count default 2 has a comparison of TEMP Sort
CBO: All_ROWS tends to tend to DISK SORT, First_ROWS tend to be with Memory but the order BY that is generally only large data will result in disk sorting,
The best way to avoid full mete scanning and sorting is to build Index
Unnecessary sorting: Missing Index: Merger Jion: Nested loops Better choices to use Distinct
