SQL素数函数

Question

如果我有一个数字X，并且想说IsPrime(X) = true/false使用sql-server，最好的方法是什么？

我只是导入素数表还是有一种算法对于较小的素数而言相当有效？

注意：我对大于约的数字不感兴趣。千万。

最终使用以下命令：

CREATE FUNCTION [dbo].[isPrime]
(
    @number INT
)
RETURNS VARCHAR(10)

BEGIN


    DECLARE @retVal VARCHAR(10) = 'TRUE';

    DECLARE @x INT = 1;
    DECLARE @y INT = 0;

    WHILE (@x <= @number )
    BEGIN

            IF (( @number % @x) = 0 )
            BEGIN
                SET @y = @y + 1;
            END

            IF (@y > 2 )
            BEGIN
                SET @retVal = 'FALSE'
                BREAK
            END

            SET @x = @x + 1

    END

    RETURN @retVal
END

Answer 1

正如您所说，您可以拥有一个表格，其中存储着最多1000万个素数。然后，查找一个数字是否为质数将是微不足道的。然后的问题是哪种方法会更快。我怀疑桌子会快很多（我还没有测试过这个说法）。

同样在这里。提供了一些解决方案。

SQL函数解决方案

解决方案0

这是通过使用Transact-SQL函数查找素数的一种解决方案：

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
–- =============================================
–- Author:        Nicolas Verhaeghe
–- Create date: 12/14/2008
–- Description:   Determines if a given integer is a prime
/*

      SELECT dbo.IsPrime(1)

      SELECT dbo.IsPrime(9)

      SELECT dbo.IsPrime(7867)

*/
–- =============================================
CREATE FUNCTION [dbo].[isPrime]
(
      @NumberToTest int
)
RETURNS bit
AS
BEGIN
      -–Declare the return variable here
      DECLARE @IsPrime bit,
                  @Divider int

      –-To speed things up, we will only attempt dividing by odd numbers

      –-We first take care of all evens, except 2
      IF (@NumberToTest % 2 = 0 AND @NumberToTest > 2)
            SET @IsPrime = 0
      ELSE
            SET @IsPrime = 1 –- By default, declare the number a prime

      –-We then use a loop to attempt to disprove the number is a prime

      SET @Divider = 3 –-Start with the first odd superior to 1

      –- We loop up through the odds until the square root of the number to test
      –- or until we disprove the number is a prime
      WHILE (@Divider <= floor(sqrt(@NumberToTest))) AND (@IsPrime = 1)
      BEGIN

            –- Simply use a modulo
            IF @NumberToTest % @Divider = 0
                  SET @IsPrime = 0
            –- We only consider odds, therefore the step is 2
            SET @Divider = @Divider + 2
      END

      –- Return the result of the function
      RETURN @IsPrime

END

解决方案1

这是通过使用一个select语句查找素数或非素数的另一种解决方案？其他评论中也有更多信息。

CREATE FUNCTION isPrime
(
    @number INT
)
RETURNS VARCHAR(10)
BEGIN
    DECLARE @prime_or_notPrime INT
    DECLARE @counter INT
    DECLARE @retVal VARCHAR(10)
    SET @retVal = 'FALSE'

    SET @prime_or_notPrime = 1
    SET @counter = 2

    WHILE (@counter <= @number/2 )
    BEGIN

        IF (( @number % @counter) = 0 )
        BEGIN
            set @prime_or_notPrime = 0
            BREAK
        END

        IF (@prime_or_notPrime = 1 )
        BEGIN
            SET @retVal = 'TRUE'
        END

        SET @counter = @counter + 1
    END
    return @retVal
END