大家好，我是考100分的小小码 ，祝大家学习进步，加薪顺利呀。今天说一说达梦dba_segments指定表名查询到的大小都包含哪些数据[亲测有效],希望您对编程的造诣更进一步.
一、结论
dba_segments指定表名查询到的段大小包含索引、约束、表字段数据（包含LOB字段）
（1）表（不包含LOB字段）创建默认分配2个簇，1个簇用于存放表结构及字段数据，1个簇用于存放cluster类型的索引
（2）创建索引默认会分配2个簇，用于存放normal索引数据
（3）创建约束不会额外分配空间，除非是主键或唯一约束
（4）添加LOB字段默认分配2个簇，用于存放lob字段数据
（5）表（包含LOB字段）创建默认分配4个簇，1个簇用于存放表结构及字段数据，1个簇用于存放cluster类型的索引，2和簇用于存放lob字段数据
二、测试过程
（一）创建测试表，查看初始大小
create table test01(id number,name varchar2(10)); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 2097152 64 2 1048576 SQL> select owner,index_name,index_type,initial_extent from dba_indexes where owner="SYSDBA" and table_name="TEST01"; OWNER INDEX_NAME INDEX_TYPE INITIAL_EXTENT ------ ------------- ---------- -------------- SYSDBA INDEX33566761 CLUSTER 1 SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name in("INDEX33566761"); 未选定行
（二）添加索引，查看空间变化
create index idx_test01_name on test01(name); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 4194304 128 4 1048576 SQL> select owner,index_name,index_type,initial_extent from dba_indexes where owner="SYSDBA" and table_name="TEST01"; OWNER INDEX_NAME INDEX_TYPE INITIAL_EXTENT ------ --------------- ---------- -------------- SYSDBA INDEX33566761 CLUSTER 1 SYSDBA IDX_TEST01_NAME NORMAL 1 SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name in("INDEX33566761","IDX_TEST01_NAME"); OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ --------------- -------------------- -------------------- -------------------- -------------------- SYSDBA IDX_TEST01_NAME 2097152 64 2 1048576
（三）添加主键，查看空间变化
alter table test01 add constraint pk_test01_id primary key(id); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 6291456 192 6 1048576 SQL> select owner,index_name,index_type,initial_extent from dba_indexes where owner="SYSDBA" and table_name="TEST01"; OWNER INDEX_NAME INDEX_TYPE INITIAL_EXTENT ------ --------------- ---------- -------------- SYSDBA INDEX33566761 CLUSTER 1 SYSDBA INDEX33566763 NORMAL 1 SYSDBA IDX_TEST01_NAME NORMAL 1 SQL> select constraint_name,constraint_type,status,index_name from dba_constraints where owner="SYSDBA" and table_name="TEST01"; CONSTRAINT_NAME CONSTRAINT_TYPE STATUS INDEX_NAME --------------- --------------- ------- ------------- PK_TEST01_ID P ENABLED INDEX33566763 SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name in("INDEX33566761","IDX_TEST01_NAME","INDEX33566763"); OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ --------------- -------------------- -------------------- -------------------- -------------------- SYSDBA IDX_TEST01_NAME 2097152 64 2 1048576 SYSDBA INDEX33566763 2097152 64 2 1048576
（四）创建约束，查看空间变化
alter table test01 add constraint ck_test01_id check(id>=1); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 6291456 192 6 1048576 SQL> select constraint_name,constraint_type,status,index_name from dba_constraints where owner="SYSDBA" and table_name="TEST01"; CONSTRAINT_NAME CONSTRAINT_TYPE STATUS INDEX_NAME --------------- --------------- ------- ------------- CK_TEST01_ID C ENABLED NULL PK_TEST01_ID P ENABLED INDEX33566763
（五）增加lob列和普通列，查看空间变化
alter table test01 add content clob; SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 8388608 256 8 1048576 alter table test01 add city varchar2(10); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST01"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST01 8388608 256 8 1048576 SQL> select id,name,crtdate from sysobjects where name="TEST01" and schid in(select id from sysobjects where name="SYSDBA" and type$="SCH"); ID NAME CRTDATE ----------- ------ -------------------------- 5751 TEST01 2022-02-22 14:55:03.347000 SQL> SELECT TABLE_USED_LOB_PAGES("SYSDBA","TEST01"); TABLE_USED_LOB_PAGES("SYSDBA","TEST01") --------------------------------------- 6 ---这个返回的是数据块，2个簇实际在用的数据块数量只有6个
（六）创建包含LOB字段的表
SQL> create table test02(id number,name varchar2(10),content clob); SQL> select owner,segment_name,bytes,blocks,extents,initial_extent from dba_segments where owner="SYSDBA" and segment_name="TEST02"; OWNER SEGMENT_NAME BYTES BLOCKS EXTENTS INITIAL_EXTENT ------ ------------ -------------------- -------------------- -------------------- -------------------- SYSDBA TEST02 4194304 128 4 1048576
作者：小丁有只猫
出处：https://www.cnblogs.com/huzei/
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原文地址：https://www.cnblogs.com/huzei/archive/2022/10/13/16788546.html
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