数据库的大小
数据库的大小主要是数据文件（dba_data_files）和临时文件(dba_temp_files;)的大小之和。
代码语言：javascript复制--查询数据文件大小
SQL> select sum(bytes) from dba_data_files;
SUM(BYTES)
----------
1515192320
--查询临时文件大小
SQL> select sum(bytes) from dba_temp_files;
SUM(BYTES)
----------
30408704
--查询数据库的大小：两项相加
SQL> select (select sum(bytes) from dba_data_files) (select sum(bytes) from dba_
temp_files) from dual;
(SELECTSUM(BYTES)FROMDBA_DATA_FILES) (SELECTSUM(BYTES)FROMDBA_TEMP_FILES)
-------------------------------------------------------------------------
1545601024
--取一个别名total_size
SQL> select (select sum(bytes) from dba_data_files) (select sum(bytes) from dba_
temp_files) as total_size from dual;
TOTAL_SIZE
----------
1545601024查询某个段对象（表，索引）的大小
dba_segments: DBA_SEGMENTSdescribes the storage allocated for all segments in the database
查看有哪些表空间
代码语言：javascript复制SQL> select tablespace_name from dba_tablespaces;
TABLESPACE_NAME
------------------------------
SYSTEM
SYSAUX
UNDOTBS1
TEMP
USERS
EXAMPLE
已选择6行。
