查询所有表名：

select t.table_name from user_tables t;

查询所有字段名：

select t.column_name from user_col_comments t;

查询指定表的所有字段名：

select t.column_name from user_col_comments t where t.table_name = 'BIZ_DICT_XB';

查询指定表的所有字段名和字段说明：

select t.column_name, t.column_name from user_col_comments t where t.table_name = 'BIZ_DICT_XB';

查询所有表的表名和表说明：

select t.table_name,f.comments from user_tables t inner join user_tab_comments f on t.table_name = f.table_name;

查询模糊表名的表名和表说明：

select t.table_name from user_tables t where t.table_name like 'BIZ_DICT%';
select t.table_name,f.comments from user_tables t inner join user_tab_comments f on t.table_name = f.table_name where t.table_name like 'BIZ_DICT%';

--查询表的数据条数、表名、中文表名

select a.num_rows, a.TABLE_NAME, b.COMMENTS
from user_tables a, user_tab_comments b
WHERE a.TABLE_NAME = b.TABLE_NAME
order by TABLE_NAME;

查找执行效率低下的SQL：

v$sqltext：存储的是完整的SQL,SQL被分割
v$sqlarea：存储的SQL 和一些相关的信息，比如累计的执行次数，逻辑读，物理读等统计信息（统计）
v$sql：内存共享SQL区域中已经解析的SQL语句。（即时）
 
 
select opname, target, to_char(start_time, 'yyyy-mm-dd hh24:mi:ss') start_time, elapsed_seconds elapsed, 
executions execs, buffer_gets/decode(executions, 0, 1, executions) bufgets, module, sql_text
from v$session_longops sl, v$sqlarea sa
where sl.sql_hash_value = sa.hash_value
and upper(substr(module, 1, 4)) <> 'RMAN'
and substr(opname, 1, 4 ) <> 'RMAN'
and sl.start_time > trunc(sysdate)
order by start_time;

根据sid查找完整sql语句：

elect sql_text from v$sqltext a where a.hash_value = (select sql_hash_value from v$session b where b.sid = '&sid')
 order by piece asc

select a.CPU_TIME,--CPU时间 百万分之一（微秒）
       a.OPTIMIZER_MODE,--优化方式
       a.EXECUTIONS,--执行次数
       a.DISK_READS,--读盘次数
       a.SHARABLE_MEM,--占用shared pool的内存多少
       a.BUFFER_GETS,--读取缓冲区的次数
       a.COMMAND_TYPE,--命令类型(3:select,2:insert;6:update;7delete;47:pl/sql程序单元)
       a.SQL_TEXT,--Sql语句
       a.SHARABLE_MEM,
       a.PERSISTENT_MEM,
       a.RUNTIME_MEM,
       a.PARSE_CALLS,
       a.DISK_READS,
       a.DIRECT_WRITES,
       a.CONCURRENCY_WAIT_TIME,
       a.USER_IO_WAIT_TIME
  from SYS.V_$SQLAREA a
 WHERE PARSING_SCHEMA_NAME = 'CHEA_FILL'--表空间
 order by a.CPU_TIME desc

从V$SQLAREA中查询最占用资源的查询：

select b.username username,a.disk_reads reads, 
    a.executions exec,a.disk_reads/decode(a.executions,0,1,a.executions) rds_exec_ratio, 
    a.sql_text Statement 
from  v$sqlarea a,dba_users b 
where a.parsing_user_id=b.user_id 
 and a.disk_reads > 100000 
order by a.disk_reads desc;
用buffer_gets列来替换disk_reads列可以得到占用最多内存的sql语句的相关信息。

列出使用频率最高的5个查询：

select sql_text,executions 
from (select sql_text,executions, 
   rank() over 
    (order by executions desc) exec_rank 
   from v$sql) 
where exec_rank <=5;

消耗磁盘读取最多的sql top5：

select disk_reads,sql_text 
from (select sql_text,disk_reads, 
   dense_rank() over 
     (order by disk_reads desc) disk_reads_rank 
   from v$sql) 
where disk_reads_rank <=5;

找出需要大量缓冲读取（逻辑读）操作的查询：

select buffer_gets,sql_text 
from (select sql_text,buffer_gets, 
   dense_rank() over 
     (order by buffer_gets desc) buffer_gets_rank 
   from v$sql) 
where buffer_gets_rank<=5;

v$sqlarea字段定义：http://happyhou.blog.sohu.com/60494432.html

`QL_TEXT`	`VARCHAR2(1000)`	First thousand characters of the SQL text for the current cursor
`SQL_ID`	`VARCHAR2(13)`	SQL identifier of the parent cursor in the library cache
`SHARABLE_MEM`	`NUMBER`	Amount of shared memory used by a cursor. If multiple child cursors exist, then the sum of all shared memory used by all child cursors.
`PERSISTENT_MEM`	`NUMBER`	Fixed amount of memory used for the lifetime of an open cursor. If multiple child cursors exist, the fixed sum of memory used for the lifetime of all the child cursors.
`RUNTIME_MEM`	`NUMBER`	Fixed amount of memory required during execution of a cursor. If multiple child cursors exist, the fixed sum of all memory required during execution of all the child cursors.
`SORTS`	`NUMBER`	Sum of the number of sorts that were done for all the child cursors
`VERSION_COUNT`	`NUMBER`	Number of child cursors that are present in the cache under this parent
`LOADED_VERSIONS`	`NUMBER`	Number of child cursors that are present in the cache and have their context heap (KGL heap 6) loaded
`OPEN_VERSIONS`	`NUMBER`	The number of child cursors that are currently open under this current parent
`USERS_OPENING`	`NUMBER`	Number of users that have any of the child cursors open
`FETCHES`	`NUMBER`	Number of fetches associated with the SQL statement
`EXECUTIONS`	`NUMBER`	Total number of executions, totalled over all the child cursors
`END_OF_FETCH_COUNT`	`NUMBER`	Number of times this cursor was fully executed since the cursor was brought into the library cache. The value of this statistic is not incremented when the cursor is partially executed, either because it failed during the execution or because only the first few rows produced by this cursor are fetched before the cursor is closed or re-executed. By definition, the value of the `END_OF_FETCH_COUNT` column should be less or equal to the value of the`EXECUTIONS` column.
`USERS_EXECUTING`	`NUMBER`	Total number of users executing the statement over all child cursors
`LOADS`	`NUMBER`	Number of times the object was loaded or reloaded
`FIRST_LOAD_TIME`	`VARCHAR2(19)`	Timestamp of the parent creation time
`INVALIDATIONS`	`NUMBER`	Total number of invalidations over all the child cursors
`PARSE_CALLS`	`NUMBER`	Sum of all parse calls to all the child cursors under this parent
`DISK_READS`	`NUMBER`	Sum of the number of disk reads over all child cursors
`DIRECT_WRITES`	`NUMBER`	Sum of the number of direct writes over all child cursors
`BUFFER_GETS`	`NUMBER`	Sum of buffer gets over all child cursors
`APPLICATION_WAIT_TIME`	`NUMBER`	Application wait time
`CONCURRENCY_WAIT_TIME`	`NUMBER`	Concurrency wait time
`CLUSTER_WAIT_TIME`	`NUMBER`	Cluster wait time
`USER_IO_WAIT_TIME`	`NUMBER`	User I/O Wait Time
`PLSQL_EXEC_TIME`	`NUMBER`	PL/SQL execution time
`JAVA_EXEC_TIME`	`NUMBER`	Java execution time
`ROWS_PROCESSED`	`NUMBER`	Total number of rows processed on behalf of this SQL statement
`COMMAND_TYPE`	`NUMBER`	Oracle command type definition
`OPTIMIZER_MODE`	`VARCHAR2(25)`	Mode under which the SQL statement was executed
`PARSING_USER_ID`	`NUMBER`	User ID of the user that has parsed the very first cursor under this parent
`PARSING_SCHEMA_ID`	`NUMBER`	Schema ID that was used to parse this child cursor
`KEPT_VERSIONS`	`NUMBER`	Number of child cursors that have been marked to be kept using the`DBMS_SHARED_POOL` package
`ADDRESS`	`RAW(4 \| 8)`	Address of the handle to the parent for this cursor
`HASH_VALUE`	`NUMBER`	Hash value of the parent statement in the library cache
`OLD_HASH_VALUE`	`NUMBER`	Old SQL hash value
`MODULE`	`VARCHAR2(64)`	Contains the name of the module that was executing at the time that the SQL statement was first parsed as set by calling `DBMS_APPLICATION_INFO`.`SET_MODULE`
`MODULE_HASH`	`NUMBER`	Hash value of the module that is named in the `MODULE` column
`ACTION`	`VARCHAR2(64)`	Contains the name of the action that was executing at the time that the SQL statement was first parsed as set by calling `DBMS_APPLICATION_INFO`.`SET_ACTION`
`ACTION_HASH`	`NUMBER`	Hash value of the action that is named in the `ACTION` column
`SERIALIZABLE_ABORTS`	`NUMBER`	Number of times the transaction fails to serialize, producing `ORA-08177` errors, totalled over all the child cursors
`CPU_TIME`	`NUMBER`	CPU time (in microseconds) used by this cursor for parsing/executing/fetching
`ELAPSED_TIME`	`NUMBER`	Elapsed time (in microseconds) used by this cursor for parsing/executing/fetching
`IS_OBSOLETE`	`VARCHAR2(1)`	Indicates whether the cursor has become obsolete (`Y` ) or not (`N` ). This can happen if the number of child cursors is too large.
`CHILD_LATCH`	`NUMBER`	Child latch number that is protecting the cursor
`PROGRAM_ID`	`NUMBER`	Program identifie

1.Oracle数据库查看用户锁表和对表解锁的sql语句

① 查看用户锁表

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

② 解锁语句

alter system kill session 'sid,serial#'

ORACLE数据库存储空间使用情况查询

使用系统sys或者dba权限的账户创建视图如下:

主要从数据库的表dba_data_files,dba_segments两张表中获取。
默认数据库保存的是byte单位，转换关系如下:
1024bytes = 1kb
1024KB = 1M
1024M = 1G

CREATE OR REPLACE VIEW V_GET_DISKSPACE AS
 SELECT A.TABLESPACE_NAME,
 A.USE "USED (MB)",
 (B.TOTAL-A.USE) "FREE (MB)",
 B.TOTAL "TOTAL (MB)",
 round((B.TOTAL-A.USE)/B.TOTAL,5)*100||'%' "PER_FREE"
 FROM
 (
 select TABLESPACE_NAME,sum(bytes)/(1024*1024) as USE from dba_segments
 /*where tablespace_name NOT IN ('USERS','SYSAUX','UNDOTBS1','SYSTEM','UNDOTBS2')*/
 GROUP BY TABLESPACE_NAME
 ) A ,
 (
 WITH TABLESPACE_TOTAL AS
 (
 SELECT tablespace_name,sum(MAXBYTES)/(1024*1024) TOTAL FROM DBA_DATA_FILES T
 WHERE /*T.TABLESPACE_NAME NOT IN ('USERS','SYSAUX','UNDOTBS1','SYSTEM','UNDOTBS2')
 AND*/ T.AUTOEXTENSIBLE='YES' group by tablespace_name
 UNION ALL
 SELECT tablespace_name,sum(bytes) TOTAL FROM DBA_DATA_FILES T
 WHERE /*T.TABLESPACE_NAME NOT IN ('USERS','SYSAUX','UNDOTBS1','SYSTEM','UNDOTBS2')
 AND*/ T.AUTOEXTENSIBLE='NO' group by tablespace_name
 )
 SELECT TABLESPACE_NAME,SUM(TOTAL) TOTAL FROM TABLESPACE_TOTAL GROUP BY TABLESPACE_NAME
 ) B
 WHERE A.TABLESPACE_NAME=B.TABLESPACE_NAME;

LINUX服务器查询

du -sch * 使用该命令查询当前目录下文件夹占用的空间的情况
df -hl 查询磁盘剩余空间

oracle常用sql 1.Oracle数据库查看用户锁表和对表解锁的sql语句

查找执行效率低下的SQL：

1.Oracle数据库查看用户锁表和对表解锁的sql语句

ORACLE数据库存储空间使用情况查询

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