SQL> create table t (a number, y number);

表已创建。

SQL> insert into t (a) select to_number(rpad('9', rownum*2, '

2 from all_objects where rownum <= 14;

已创建14行。

SQL> update t set y = a + 1;

已更新14行。

SQL> select a, y ,vsize(a) v1, vsize(y) v2 from t order by a;

A Y V1 V2

------------------------------ ------------------------------ --- ---

99 100 2 2

9999 10000 3 2

999999 1000000 4 2

99999999 100000000 5 2

9999999999 10000000000 6 2

999999999999 1000000000000 7 2

99999999999999 100000000000000 8 2

9999999999999999 10000000000000000 9 2

999999999999999999 1000000000000000000 10 2

99999999999999999999 100000000000000000000 11 2

9999999999999999999999 10000000000000000000000 12 2

A Y V1 V2

------------------------------ ------------------------------ --- ---

999999999999999999999999 1000000000000000000000000 13 2

99999999999999999999999999 100000000000000000000000000 14 2

9999999999999999999999999999 10000000000000000000000000000 15 2

可以发现，Y始终占2个字节，A每增加2位有效数字就增加1个字节。number类型存储的是有效数字和小数点的位置，所以有效数字越多占用的空间越大。

ITPub博客

number占用的空间