一些实用的DBA语句（持续学习，持续更新）

--查询LOB的大小和所在表空间

SELECT A.TABLE_NAME,
A.COLUMN_NAME,
B.SEGMENT_NAME,
B.SEGMENT_TYPE,
B.TABLESPACE_NAME,
round((B.BYTES / 1024 / 1024 / 1024),2)
FROM USER_LOBS A, USER_SEGMENTS B
WHERE A.SEGMENT_NAME = B.SEGMENT_NAME
ORDER BY B.BYTES DESC;

--查询查询一个表空间上所有表的大小
select us.segment_name, us.segment_type,us.tablespace_name,
us.tablespace_name,
round((us.BYTES/1024/1024/1024),2)
from user_segments us
where us.tablespace_name = '';

--查询特定一些表的大小，可以更换查询关键字
select segment_name,
alt.OWNER
tablespace_name,
segment_type,
round((BYTES /1024/1024/1024), 2) as "大小（GB）"
from user_segments, all_tables alt
where segment_type = 'TABLE'
and segment_name like '%%'
and alt.TABLE_NAME = segment_name
order by tablespace_name, BYTES desc;

--查询当前表空间的使用情况
SELECT a.tablespace_name "表空间名",
total/1024/1024 表空间大小,
trunc((free/1024/1024),2) 表空间剩余大小,
trunc(((total - free)/1024/1024),2) 表空间使用大小,
ROUND((total - free) / total, 4) * 100 "使用率%"
FROM (SELECT tablespace_name, SUM(bytes) free
FROM DBA_FREE_SPACE
GROUP BY tablespace_name) a,
(SELECT tablespace_name, SUM(bytes) total
FROM DBA_DATA_FILES
GROUP BY tablespace_name) b
WHERE a.tablespace_name = b.tablespace_name;

/*查询锁表情况*/
select sess.sid,
sess.serial#,
lo.oracle_username,
lo.os_user_name,
ao.object_name,
lo.locked_mode
from v$locked_object lo,
dba_objects ao,
v$session sess
where ao.object_id = lo.object_id and lo.session_id = sess.sid

　　

/*1 统计数据表的num_row
2 统计索引列的distinct_keys
3 计算distinct_keys/num_rows的值，
该值越接近1，则列的选择度越高，
索引的效率就越高*/

analyze table schema.tablename compute statistics for all indexes for all columns; --收集最新的信息

select ut.num_rows, ui.distinct_keys, round((ui.distinct_keys/ut.num_rows), 2)
from user_indexes ui,
user_tables ut
where ui.table_name = upper('tablename')
and ui.index_name = upper('indexname')
and ut.table_name = ui.table_name;

/*比较笨的办法，纯手工统计，计算*/
select count(*) from schema.tablename; --统计出了表的总行数
select distinct(ind_row) from schema.tablename; --统计索引所在列的distinct值
--之后就是纯手工计算了

/*查询等待事件*/
SELECT event,
sum(decode(wait_time, 0, 1, 0)) "当前等待",
sum(decode(wait_time, 0, 0, 1)) "当前未在等待",
count(*) "Total"
FROM v$session_wait
GROUP BY event
ORDER BY count(*) desc;

select a.EVENT, count(*)
from v$session_wait a
group by a.EVENT, a.WAIT_CLASS#
order by count(*) desc;

--查询占用UNDO的用户相关情况
SELECT S.USERNAME, U.NAME, S.SID, S.SERIAL#
FROM V$TRANSACTION T, V$ROLLSTAT R, V$ROLLNAME U, V$SESSION S
WHERE S.TADDR = T.ADDR
AND T.XIDUSN = R.USN
AND R.USN = U.USN
ORDER BY S.USERNAME;

　　--锁定、解锁账户语句

alter user username account lock;

alter user username account unlock;

--修改用户密码，如果遇到ORA-28001错误也可如此解决

alter user username identified by password;

--手工扩大一个数据文件

alter database datafile '/data/data_file1.dbf' resize 10G;