1 概述

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伪列

rownum：记录的编号

会变化，如：使用 order by 时

rowid：记录的物理地址

不变化，除非 row movement

编号有 1 才有 2。rownum >=2 无数据返回

基于 64 位编码的 18 个字符显示

2 详解

2.1 rownum

select t.empno, t.ename, t.hiredate, rownum from scott.emp t;select t.empno, t.ename, t.hiredate, rownum from scott.emp t order by t.hiredate;

查询截图：（rownum 不一定是连续的哦）

原因：sql 语句执行顺序：先 select 后 order by
解决：再嵌套查询一次，如：select rownum from (上述)
扩展：Oracle sql 语句执行顺序【面试题】

2.2 rowid

select rowid, -- base 64位 编码，18 个字符显示-- 数据对象: dba_objects.object_iddbms_rowid.rowid_object(rowid) object_id,-- 相对文件: dba_data_files.relative_fnodbms_rowid.rowid_relative_fno(rowid) relative_fno,-- 数据块: dba_extents.(block_id + blocks - 1)dbms_rowid.rowid_block_number(rowid) block_number, -- 行: dba_tab_columns.column_id dbms_rowid.rowid_row_number(rowid) row_numberfrom scott.emp;

查询截图：

解释说明：

base 64 编码
A-Z 0-25
a-z 26-51
0-9 52-61
+/ 62-63计算公式：d*(b^p)
d: 字符对应的十进制编码值
b: 64
p: 从右至左，每个对象从 0 开始计数AAAR3sAAEAAAACXAAA
数据对象id（6位）：AAAR3s0*64^5 + 0*64^4 + 0*64^3 + 17*64^2 + 54*64^1 + 44*64^0 = 73196文件id（3位）：AAE0*64^2 + 0*64^1 + 4*64^0 = 4块id（6位）：AAAACX2*64^1 + 23 = 151 行id（3位）：AAA = 0

base 64 码表：

索引	字符	索引	字符	索引	字符	索引	字符
0	A	26	a	52	1	62	+
1	B	27	b	53	2	63	/
2	C	28	c	54	3
3	D	29	d	55	4
4	E	30	e	56	5
5	F	31	f	57	6
6	G	32	g	58	7
7	H	33	h	59	8
8	I	34	i	60	9
9	J	35	j
10	K	36	k
11	L	37	l
12	M	38	m
13	N	39	n
14	O	40	o
15	P	41	p
16	Q	42	q
17	R	43	r
18	S	44	s
19	T	45	t
20	U	46	u
21	V	47	v
22	W	48	w
23	X	49	x
24	Y	50	y
25	Z	51	z

3 扩展

3.1 Oracle 分页查询详解（rownum 实现）

Oracle 分页查询详解（rownum 实现）

3.2 Oracle 高效删除重复数据（rowid）

Oracle 高效删除重复数据（rowid）

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