Drop Table会释放所占segment的空间，而数据文件占用OS空间不变
一.创建表空间，表，插入300条数据
1 SQL> create tablespace tbs datafile '/opt/oracle/oradata/nwom/TEST_TBS.dbf' size 1m autoextend off; 2 3 Tablespace created. 4 5 SQL> create table t1 (a char(2000)) tablespace tbs; 6 7 Table created. 8 9 --插入300条数据 10 SQL> begin 11 2 for i in 1..300 loop 12 3 insert into t1 values('a'); 13 4 end loop; 14 5 end; 15 6 / 16 17 PL/SQL procedure successfully completed. 18 19 SQL> commit; 20 21 Commit complete. 22 23 SQL> select count(*) from t1; 24 25 COUNT(*) 26 ---------- 27 300
二.查看表所占用的segment
1 --300条数据占用段0.9375M 2 SQL> col SEGMENT_NAME format a10; 3 SQL> col SEGMENT_TYPE format a20 4 SQL> col TABLESPACE_NAME format a20 5 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)" 6 2 from user_segments where segment_name='T1'; 7 8 SEGMENT_NA SEGMENT_TYPE TABLESPACE_NAME SIZE(M) 9 ---------- -------------------- -------------------- ---------- 10 T1 TABLE TBS .9375 11 12 SQL>
三.Drop Table
1 SQL> drop table t1; 2 3 Table dropped.
四.Drop Table后，查看表所占用的segment
1 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)" 2 2 from user_segments where segment_name='T1'; 3 4 no rows selected
五.重新建表t1，插入数据100条
1 SQL> create table t1 (a char(2000)) tablespace tbs; 2 3 Table created. 4 5 --插入100条数据 6 SQL> begin 7 2 for i in 1..100 loop 8 3 insert into t1 values('a'); 9 4 end loop; 10 5 end; 11 6 / 12 13 PL/SQL procedure successfully completed. 14 15 SQL> commit; 16 17 Commit complete. 18 19 20 SQL> select count(*) from t1; 21 22 COUNT(*) 23 ---------- 24 100
六.查看表t1所占用segment
1 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)" 2 2 from user_segments where segment_name='T1'; 3 4 SEGMENT_NA SEGMENT_TYPE TABLESPACE_NAME SIZE(M) 5 ---------- -------------------- -------------------- ---------- 6 T1 TABLE TBS .3125 7 8 SQL>
结论：对比二与六的size(M)，可知Drop Table会释放表占用的segment。