select case when a.cnt = b.cnt then '两个库结构一致' 
when a.cnt <> b.cnt then '两个库结构不一致' end 
from (select count(*) as cnt 
from dba_tab_columns t1, dba_tab_columns@lnk_db2 t2 
where t1.owner = 'TAOBAO' 
and t1.owner = t2.owner 
and t1.table_name = t2.table_name 
and t1.column_name = t2.column_name 
and t1.data_type = t2.data_type 
and t1.data_length = t2.data_length 
and t1.nullable = t2.nullable 
and nvl(t1.data_precision, 0) = nvl(t2.data_precision, 0) 
and nvl(t1.data_scale, 0) = nvl(t2.data_scale, 0)) a, 
(select count(*) as cnt 
from dba_tab_columns 
where owner = 'TAOBAO') b