テーブルを使用してクエリを選択して結合する方法

グループ化括弧のほとんどを削除できるはずです...

select *
from
    (select 'Source1' Source from Dual
     union select 'Source2' from Dual
     union select 'Source3' from Dual
     union select 'Source4' from Dual
     ) s
    cross join (
      select 'O' Status from Dual
      union select 'C' from Dual
     ) x
    cross join (
      SELECT
      TO_DATE('09/30/2013','mm/dd/yyyy') - 1 + LEVEL dt
      FROM dual
      CONNECT BY
      LEVEL <= ( TO_DATE('10/05/2013','mm/dd/yyyy')
           - TO_DATE('09/30/2013','mm/dd/yyyy')) + 1
     ) d
left join 
    myTable y
on y.err_sts_cd = x.Status