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Home > Articles > Transact SQL Programming Articles

Generating Random Strings of Characters in Transact-SQL

The following Transact SQL procedure can be used to generate a random string of characters. As such it can be used to for example generate a default password for a user. The specific characters that are used to generate the string can be specified, so it can be customised (e.g. to only create passwords of digits or lower cased letters). The length of the generated random string can also be specified.

It is recommended that this SQL procedure be used as a stored procedure.

Using as a Stored Procedure

The following stored procedure creates a random string of characters of a length specified by the parameter @Length:

CREATE PROCEDURE sp_GeneratePassword
(
    @Length int
)

AS

DECLARE @RandomID varchar(32)
DECLARE @counter smallint
DECLARE @RandomNumber float
DECLARE @RandomNumberInt tinyint
DECLARE @CurrentCharacter varchar(1)
DECLARE @ValidCharacters varchar(255)
SET @ValidCharacters = '
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+&$'
DECLARE @ValidCharactersLength int
SET @ValidCharactersLength = len(@ValidCharacters)
SET @CurrentCharacter = ''
SET @RandomNumber = 0
SET @RandomNumberInt = 0
SET @RandomID = ''

SET NOCOUNT ON

SET @counter = 1

WHILE @counter < (@Length + 1)

BEGIN

        SET @RandomNumber = Rand()
        SET @RandomNumberInt = Convert(tinyint, ((@ValidCharactersLength - 1) * @RandomNumber + 1))

        SELECT @CurrentCharacter = SUBSTRING(@ValidCharacters, @RandomNumberInt, 1)

        SET @counter = @counter + 1

        SET @RandomID = @RandomID + @CurrentCharacter

END

SELECT @RandomID AS 'Password'
GO

Useful Links

  • The SQL Documentation Tool builds technical documentation for Microsoft SQL Server databases. A free trial version is available for download.

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