Fungsi bilangan prima SQL

Anda dapat, seperti yang Anda katakan, memiliki tabel yang menyimpan semua bilangan prima hingga 10 juta . Maka akan sepele untuk mencari apakah suatu bilangan prima atau tidak. Pertanyaannya kemudian adalah metode mana yang lebih cepat. Saya menduga tabelnya akan jauh lebih cepat (saya belum menguji klaim ini).

Solusi Tabel Utama

• https:// www.simple-talk.com/sql/t-sql-programming/celkos-summer-sql-stumpers-prime-numbers/
  Memberikan beberapa solusi dan masih banyak lagi di komentar.

• https:// sqlserverfast.com/blog/hugo/2006/09/the-prime-number-challenge-great-waste-of-time/
  Sama di sini. Beberapa solusi disediakan.

Solusi Fungsi SQL

Inilah salah satu solusi melalui Menemukan bilangan prima dengan fungsi Transact-SQL :

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

Berikut solusi lain melalui bagaimana menemukan apakah itu prima atau bukan prima dengan satu pernyataan pilih? Ada lebih banyak informasi di komentar lain juga.

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