三个随机产生密码的存储过程

协助一个朋友做一个小网站，其中一个功能，是让用户注册成功之后，系统将随机产生一个登录密码，并自动发送至注册邮箱中，朋友的做法是为了用户使用真实邮箱。

随机产生密码，Insus.NET总结了三个，并分别写成了存储过程。

第一个，

CREATE PROCEDURE [dbo].[usp_RandomPassword] 
(
   @Length INT = 8
)
AS
BEGIN      
    DECLARE @RandomPassword NVARCHAR(MAX) = N'',@L INT = 1
    WHILE @L <= @Length  --循环密码长度
    BEGIN
        --随机产生每一位字符，ASCII码48至122
        DECLARE @RndChar CHAR(1) = CHAR(ROUND(RAND() * (122-48+1) + 48,0))
        --随机产生的字符不包括下面字符
        IF ASCII(@RndChar) NOT IN(58,59,60,61,62,63,64,91,92,93,94,95,96) -- : , ; , < , = , > , ? ,@ , [ , \ , ] , ^ , _ , `
        BEGIN
            SET @RandomPassword = @RandomPassword + @RndChar
            SET @L = @L + 1
        END        
    END
    SELECT @RandomPassword
END

第二个，

CREATE PROCEDURE [dbo].[usp_RandomPassword] 
(
   @Length INT = 8
)
AS
BEGIN  
    DECLARE @RandomPassword NVARCHAR(MAX) = N'',@L INT = 1
    --随机密码将由下面字符串产生，数字0-9,大写字母A-Z,小写字母a-z
    DECLARE @BaseString VARCHAR(255) = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'  
    WHILE @L <= @Length --循环密码长度
    BEGIN
        --61是变量@BaseString的长度减一
        SET @RandomPassword = @RandomPassword + SUBSTRING(@BaseString, CONVERT(INT,ROUND(RAND() * 61 + 1,0)),1)
        SET @L = @L + 1
    END
    SELECT @RandomPassword
END

第三个，

CREATE PROCEDURE [dbo].[usp_RandomPassword] 
(
   @Length INT = 8
)
AS
BEGIN  
    DECLARE @RandomPassword NVARCHAR(MAX) = N'' 
    DECLARE @R TINYINT,@L INT = 1      
    WHILE  @L <= @Length --循环密码长度
    BEGIN
        SET @R = ROUND(RAND() * 2, 0)    --随机产生0,1,2整数
        IF @R = 0 --当变量为0时，将随机产生一位数字
            SET @RandomPassword = @RandomPassword + CHAR(ROUND(RAND() * 9 + 48,0)) 
        ELSE IF @R = 1 --当变量为1时，将随机产生一位大写字母
            SET @RandomPassword = @RandomPassword + CHAR(ROUND(RAND() * 25 + 65,0)) 
        ELSE IF @R = 2 --当变量为2时，将随机产生一位小写字母
            SET @RandomPassword = @RandomPassword + CHAR(ROUND(RAND() * 25 + 97,0))            
        SET @L = @L + 1
    END
    SELECT @RandomPassword
END

最后一个也可以重构写成：

CREATE PROCEDURE [dbo].[usp_RandomPassword] 
(
   @Length INT = 8
)
AS
BEGIN  
    DECLARE @RandomPassword  NVARCHAR(MAX) = N'',@L INT = 1   
    WHILE @L <= @Length --循环密码长度
    BEGIN         
        DECLARE @R INT = ROUND(RAND() * 2, 0) 
        SET @RandomPassword = @RandomPassword + CASE @R
        WHEN 0 THEN CHAR(ROUND(RAND() * 9 + 48,0)) 
        WHEN 1 THEN CHAR(ROUND(RAND() * 25 + 65,0)) 
        WHEN 2 THEN CHAR(ROUND(RAND() * 25 + 97,0)) END                            
        SET @L = @L + 1        
    END
    SELECT @RandomPassword
END

Also reference:

MS SQL随机数  http://www.cnblogs.com/insus/archive/2012/01/27/2330058.html

不重复的随机数 http://www.cnblogs.com/insus/archive/2012/01/27/2330104.html