Dynamical sql to drop all disks from an ASM disk group

set pagesize 0

select 'ALTER DISKGROUP '||  dg.name || ' DROP DISK '|| d.name || ';' 
from v$asm_disk d join v$asm_diskgroup dg
on (d.group_number = dg.group_number)
where dg.name = '&diskgroup_name';