Dovrebbe funzionare (funziona per me)
update table_a outer
set sequence_column = (
select rnum from (
-- evaluate row_number() for all rows ordered by your columns
-- BEFORE updating those values into table_a
select id, row_number() over (order by column1, column2) rnum
from table_a) inner
-- join on the primary key to be sure you'll only get one value
-- for rnum
where inner.id = outer.id);
O usi il MERGE dichiarazione. Qualcosa del genere.
merge into table_a u
using (
select id, row_number() over (order by column1, column2) rnum
from table_a
) s
on (u.id = s.id)
when matched then update set u.sequence_column = s.rnum
