Oracle中实现圆周率计算(三


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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