1.创建测试表
SQL> create table t1 (id int);
Table created.
2.查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
3.对T1表做统计信息收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;
Table analyzed.
4.再次查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
0 7 0
5.向表中插入1000W条数据
declare
i number;
begin
for i in 1..10000000 loop
insert into t1 values(i);
end loop;
commit;
end;
/
6.查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
0 7 0
7.统计信息收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;
Table analyzed.
8.再次查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
15155 204 10000000
9.删除数据
SQL> delete from t1;
10000000 rows deleted.
SQL> commit;
Commit complete.
10.查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
15155 204 10000000
11.统计信息收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;
Table analyzed.
12.再次查看表占用的块数量，可以看到
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
15155 204 0
13.降低高水位操作
SQL> alter table T1 move;
Table altered.
14.再次查看表占用的块数量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
15155 204 0
15.再次收集统计信息
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;
Table analyzed.
16.查看表占用的块数量，可以看到执行alter table T1 move命令后，高水位已经下降了。
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
0 7 0
4种降低高水位的方法：
ANALYZE TABLE T1 COMPUTE STATISTICS; 分析表
SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1'; 查询高水位线方法
1：alter table T1 enable row movement; 开启行迁移(收缩表操做第一步)
alter table T1 shrink space ; 收缩表空间
alter table T1 disable row movement; 关闭行迁移方法
2：alter table T1 move; 移动表需要新建索引
create Index new_index On T1(deptno); 单一索引
create Index new_index on T1(deptno,job); 复合索引方法
3：truncate table T1; 清空表方法
4：create table T1_NEW as select * from T1 where 1=2;
创建新表alter table T1_NEW rename to T1; 重命名新表
