主要是在Oracle中经常会遇到的问题的一个总结.
  在oracle中number表示数据型,p=>pricesion,s=>scale.在oracle管方网站上对number(p,s),作以下的解释:

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The NUMBER datatype stores zero as well as positive and negative fixed numbers with absolute values from 1.0 x 10^-130 to (but not including) 1.0 x 10¹²⁶. If you specify an arithmetic expression whose value has an absolute value greater than or equal to 1.0 x 10¹²⁶, then Oracle returns an error. Each NUMBER value requires from 1 to 22 bytes.

Specify a fixed-point number using the following form:

NUMBER(p,s)

where:

• p is the precision, or the total number of significant decimal digits, where the most significant digit is the left-most nonzero digit, and the least significant digit is the right-most known digit. Oracle guarantees the portability of numbers with precision of up to 20 base-100 digits, which is equivalent to 39 or 40 decimal digits depending on the position of the decimal point.

• s is the scale, or the number of digits from the decimal point to the least significant digit. The scale can range from -84 to 127.

  • Positive scale is the number of significant digits to the right of the decimal point to and including the least significant digit.

  • Negative scale is the number of significant digits to the left of the decimal point, to but not including the least significant digit. For negative scale the least significant digit is on the left side of the decimal point, because the actual data is rounded to the specified number of places to the left of the decimal point. For example, a specification of (10,-2) means to round to hundreds.

Scale can be greater than precision, most commonly when e notation is used. When scale is greater than precision, the precision specifies the maximum number of significant digits to the right of the decimal point. For example, a column defined as NUMBER(4,5) requires a zero for the first digit after the decimal point and rounds all values past the fifth digit after the decimal point.

It is good practice to specify the scale and precision of a fixed-point number column for extra integrity checking on input. Specifying scale and precision does not force all values to a fixed length. If a value exceeds the precision, then Oracle returns an error. If a value exceeds the scale, then Oracle rounds it.
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太长了,看不是太懂.
总结一下:
1,范围:number(p,s)
    a,p在1~38,s在-84~127
2,p>s时:
    a,s>0时:
       数据的有效数字为p个,小数部分为s个,整数部分为p-s个
       如果整数大于p-s时,报错;
       如果小数部分大于s,会对小数部分四舍五入,最后变成s.    
    b,s=0时:表示这个没有小数的数(可以理解为整形)
    c,s<0时:表示这个是整形(没有小数位)
       从小数点左起每|s|个位进行四舍五入,
        然后整数的有效位数为p+|s|位,如果整数的数据大于p+|s|时,会报错.       
3,p     a,小数起必须要存在s-p个0,如果不够,会报错;
    b,小数位数大于s,会自动四舍五入;

参考一下: http://hi.baidu.com/mars_mars/blog/item/6154198083d989d2bd3e1eae.html
          http://www.cnblogs.com/hengzi/archive/2011/08/17/Oracle-10g-datatype.html