NUMBER Data Type

The NUMBER data type stores fixed and floating-point numbers. The database can store numbers of virtually any magnitude(大小). This data is guaranteed to be portable among different operating systems running Oracle Database. The NUMBER data type is recommended for most cases in which you must storenumeric(数) data.

You specify a fixed-point number in the form NUMBER(p,s), where p and s refer to the following characteristics:

• Precision

  The precision specifies the total number of digits. If a precision is not specified, then the column stores the values exactly as provided by the application without any rounding.

• Scale

  The scale specifies the number of digits from the decimal(小数) point to the least significant digit. Positive scale counts digits to the right of the decimal point up to and including the least significant digit. Negative scale counts digits to the left of the decimal point up to but not including the least significant digit. If you specify a precision without a scale, as in NUMBER(6), then the scale is 0.

In Example 2-1, the salary column is type NUMBER(8,2), so the precision is 8 and the scale is 2. Thus, the database stores a salary of 100,000 as 100000.00.

Number having precision p and scale s. The precision p can range from 1 to 38. The scale s can range from -84 to 127. Both precision and scale are in decimal digits. A NUMBER value requires from 1 to 22 bytes.

最高整数位数 ＝ p - s  # The precision specifies the total number of digits.
s正数，小数点右边指定位置开始四舍五入 
s负数，小数点左边指定位置开始四舍五入 
s是0或者未指定，四舍五入到最近整数 
当p小于s时候，表示数字是绝对值小于1的数字，且从小数点右边开始的前s-p 位必须是0，保留s位小数。 
p 效数位：从左边第一个不为0的数算起
如 0.01234567 NUMBER(4,5) 其实存储结果为 0.01235

p>0，对s分2种情况： 
1. s>0 
精确到小数点右边s位，并四舍五入。然后检验有效数位是否<=p；如果s>p，小数点右边至少有s-p个0填充。 
2. s<0 
精确到小数点左边s位，并四舍五入。然后检验有效数位是否<=p+|s| 

Value     Datatype     Stored Value 
123.2564    NUMBER    123.2564 
1234.9876    NUMBER(6,2)    1234.99 
12345.12345    NUMBER(6,2)    Error 
1234.9876    NUMBER(6)    1235 
12345.345    NUMBER(5,-2)    12300 
1234567    NUMBER(5,-2)    1234600 
12345678    NUMBER(5,-2)    Error 
123456789    NUMBER(5,-4)    123460000 
1234567890    NUMBER(5,-4)    Error 
12345.58    NUMBER(*, 1)    12345.6 
0.1    NUMBER(4,5)    Error 
0.01234567    NUMBER(4,5)    0.01235 
0.09999    NUMBER(4,5)    0.09999 
0.099996    NUMBER(4,5)    <>