SQL Prime编号功能

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

我只是导入一个素数表还是有一个算法对于较小的素数是相当有效的？

注意：我对大于约的数字不感兴趣.千万.

结束使用以下内容：

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

解决方法

Prime Table解决方案

> https://www.simple-talk.com/sql/t-sql-programming/celkos-summer-sql-stumpers-prime-numbers/提供一些解决方案,评论中还有更多.
> http://sqlblog.com/blogs/hugo_kornelis/archive/2006/09/23/Prime-numbers.aspx
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Finding prime numbers with a Transact-SQL function的一个解决方案：

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how to find whether is a prime or non prime with one select statement?的另一个解决方案.其他评论中还有更多信息.

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

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