oracle decode函数，不管查询的结果是否满足‘PRIMARY’，参数中的select语句还是会执行的,通过查看执行计划就知道
set autotrace traceonly
select decode(database_role ,'PRIMARY',
(select
trunc((size_MB-free_MB)*100/maxsize_MB) "retvalue"
from (
select
tablespace_name,case when sum(decode(autoextensible,'YES',1,0))>0 then 'YES'
else 'NO' end ext,
trunc(sum(bytes)/1024/1024) SIZE_MB,
trunc(sum(case when autoextensible='YES' then maxbytes else bytes
end)/1024/1024) MAXSIZE_MB
from dba_data_files
group by tablespace_name
) t1,
(
select tablespace_name,trunc(sum(bytes)/1024/1024) FREE_MB
from dba_free_space
group by tablespace_name
) t2,
(select tablespace_name
from dba_tablespaces
where contents='PERMANENT') t3
where t1.tablespace_name=t2.tablespace_name and t3.tablespace_name=t1.tablespace_name and t3.tablespace_name='SYSTEM'),0) as retvalue from v$database;decode函数等价于cash when语句，只不过当条件比较多时，decode函数书写起来比较简洁一点而已
select case
when database_role = 'PRIMARY' then (select tname from tab where rownum=1)
else '0'
end as retvalue
from v$database;免责声明：本站发布的内容（图片、视频和文字）以原创、转载和分享为主，文章观点不代表本网站立场，如果涉及侵权请联系站长邮箱：is@yisu.com进行举报，并提供相关证据，一经查实，将立刻删除涉嫌侵权内容。
