Oracle Rownum SQL -


what differences (advantages , disadvantages) between these 2 coding techniques?

select * (     select rownum rnun, * table rownum < x ) rnum > y   select * (     select * table ) rownum < x , x > y

the 2 queries return different rows.

neither query deterministic. neither query should ever used in real system.

the first query appears @ least attempt generate window of rows (rows between x , y). since there no order by, however, order of rows not deterministic , window doesn't want.

the second query returns arbitrary x rows of data (assuming x > y). otherwise returns 0 rows (if y >= x). if you're trying build sort of windowing query, isn't it.

if want windowing query works, you'd want like

select *   (select a.*,                row_number() on (order something) rnum           table_name)  rnum between x , y

if wanted use rownum, you'd need like

select *   (select a.*,                rownum rnum           from( select b.*                   table_name                  order something) a)  rownum < y    , rnum > x

but tends less efficient analytic query approach.


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