select 'alter table '||table_name||' modify '||column_name||' '||data_type||'('||data_length||' char);'
from USER_TAB_COLUMNS
where data_type='VARCHAR2'
and table_name in(select table_name from USER_ALL_TABLES)
select 'alter table '||table_name||' modify '||column_name||' '||data_type||'('||data_length||' char);'
from USER_TAB_COLUMNS
where data_type='VARCHAR2'
and table_name in(select table_name from USER_ALL_TABLES)