【Oracle】-【插入读取顺序】-插入读取之间的顺序关系

Oracle插入记录的顺序是否是读取的顺序？

通过一个简单的实验验证：

SQL> create table t
( x int,
a char(2000) default 'x',
b char(2000) default 'x',
c char(2000) default 'x');
Table created.

SQL> insert into t (x) values ( 1 );
1 row created.

SQL> insert into t (x) values ( 2); 
1 row created.

SQL> insert into t (x) values ( 3); 
1 row created.

SQL> commit;
Commit complete.

SQL> select x, rownum, rowid from t; 
         X     ROWNUM ROWID
---------- ---------- ------------------
         3          1 AAAOXNAAHAAAAasAAA
         1          2 AAAOXNAAHAAAAavAAA
         2          3 AAAOXNAAHAAAAawAAA


SQL> delete from t where x = 2;
1 row deleted.

SQL> commit;
Commit complete.

SQL> select x, rownum, rowid from t; 
         X     ROWNUM ROWID
---------- ---------- ------------------
         3          1 AAAOXNAAHAAAAasAAA
         1          2 AAAOXNAAHAAAAavAAA

SQL> insert into t (x) values ( 4 );
1 row created.


SQL> select x, rownum, rowid from t; 
         X     ROWNUM ROWID
---------- ---------- ------------------
         3          1 AAAOXNAAHAAAAasAAA
         1          2 AAAOXNAAHAAAAavAAA
         4          3 AAAOXNAAHAAAAawAAA

insert into t (x) values ( 5);


SQL> select x, rownum, rowid from t; 

         X     ROWNUM ROWID
---------- ---------- ------------------
         3          1 AAAOXNAAHAAAAasAAA
         5          2 AAAOXNAAHAAAAatAAA
         1          3 AAAOXNAAHAAAAavAAA
         4          4 AAAOXNAAHAAAAawAAA

SQL> insert into t (x) values ( 10);
1 row created.

SQL> select x, rownum, rowid from t; 
         X     ROWNUM ROWID
---------- ---------- ------------------
         3          1 AAAOXNAAHAAAAasAAA
         5          2 AAAOXNAAHAAAAatAAA
        10          3 AAAOXNAAHAAAAauAAA
         1          4 AAAOXNAAHAAAAavAAA
         4          5 AAAOXNAAHAAAAawAAA

可见Oracle读取时按照记录的ROWID默认升序排列的，Oracle是一种堆表(默认)，堆的意思就是杂乱无章的，插入数据时是根据内部算法，找到可用的数据块，一般出于效率的考虑，不采用原来的空间，用逻辑块的新空间，读取的顺序与COMMIT也没有直接关系，所以要排序，最好用ORDER BY。