Oracle SQLの置換機能

それは本当に 変。代わりに、逆の順序で並べ替えてみましょう:

select replace(replace('count(distinct <thiscol>) over (partition by <nextcol>) / count(*) over () as <thiscol>_<nextcol>,',
                       '<thiscol>', column_name
                      ), '<nextcol>', lead(column_name) over (order by column_id desc)
              )
from all_tab_columns atc
where table_name = 'mytable';
  

 desc に注意してください