--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 BWHERE A.SEGMENT_NAME = B.SEGMENT_NAMEORDER 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;<br><br>--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 SWHERE S.TADDR = T.ADDRAND T.XIDUSN = R.USNAND R.USN = U.USNORDER 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;?