上一篇文章提到,Oracle的NUMBER类型精度只有38位,因此想要确保100位的精度就无法直接使用Oracle的NUMBER类型来实现了。
如果在Oracle希望实现这个功能,那么最简单的办法莫过于使用JAVA存储过程了,下面算法不变,将代码迁移到JAVA存储过程中:
SQL> create or replace and compile java source named "pi" as
2 import java.math.BigDecimal;
3 public class pi extends Object
4 {
5 public static String pi (int n)
6 {
7 BigDecimal result = new BigDecimal(1);
8 for (int i=n;i>0;i--)
9 {
10 BigDecimal temp = new BigDecimal(i);
11 result = new BigDecimal(2).add
12 (result.multiply
13 (temp.divide(new BigDecimal(1).add
14 (temp.multiply
15 (new BigDecimal(2))
16 ),102,BigDecimal.ROUND_HALF_UP)
17 )
18 );
19 }
20 return result.toString().substring(0,102);
21 }
22 }
23 /
Java 已创建。
建立存储过程后,在建立一个PL/SQL函数接口:
SQL> create or replace function f_pi (p_n in number) return varchar2 as
2 language java name 'pi.pi(int) return String';
3 /
函数已创建。
下面就可以调用这个JAVA存储过程进行运算了:
SQL> SELECT F_PI(10) FROM DUAL;
F_PI(10)
--------------------------------------------------------------------------------------------------------
3.1408420956408572507643715074055631331173126838761513684114303309349748978231950368173278389996656250
SQL> SELECT F_PI(100) FROM DUAL;
F_PI(100)
--------------------------------------------------------------------------------------------------------
3.1415926535897932384626433832792952864908441267910666216977616133327809721178539595244159254337299498
在多项式N达到330的时候,返回的圆周率精度到了100位。
SQL> SELECT F_PI(329) FROM DUAL;
F_PI(329)
--------------------------------------------------------------------------------------------------------
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170678
SQL> SELECT F_PI(330) FROM DUAL;
F_PI(330)
--------------------------------------------------------------------------------------------------------
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679
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