Default random 10 character string value for SQL Server column

Question

I have a column rndm in my table [guests]. Now, for the field Default value or Binding for the table, whenever a new row is inserted I want to automatically insert a 10-character random string into this column as the default value.

This random string may not contain special characters, only characters from a-zA-Z0-9. What is the best approach to achieve this?

To be clear: I don't want to generate this random string in my .NET code, I want it to be generated within SQL Server. And I want to paste this string generation directly into the field Default value or Binding for the table, so not a separate SQL statement. So for example like it works when pasting getdate() into the field Default value or Binding.

Answer 1

Expanding on what Deigo Garbar has already suggested.

If you want to use the expression as the default value in your table you would need to put this expression in a function.

But the problem is a UDF function will not allow you to use NEWID() function in it, it will complain about cannot use non-deterministic function in UDF bla bla....

A way around will be to create a view first which simply calls this expression then use that view inside your function and then use that function as Default value for your table.

View

CREATE VIEW dbo.vw_Function_Base
AS
SELECT substring(replace(convert(varchar(100), NEWID()), '-', ''), 1, 10) AS Rand_Value

Function

CREATE FUNCTION dbo.fn_getRandom_Value()
RETURNS VARCHAR(10)
AS
BEGIN
  DECLARE @Rand_Value VARCHAR(10);
SELECT @Rand_Value = Rand_Value
FROM vw_Function_Base

  RETURN @Rand_Value;
END

Now you can use this function as default value in your table.

Test

CREATE TABLE SomeTest_Table
 ( ID        INT
 , RandValue VARCHAR(10) DEFAULT dbo.fn_getRandom_Value()
 )
GO

 INSERT INTO SomeTest_Table(ID)
 VALUES (1)
GO

 SELECT * FROM SomeTest_Table

Important Note

I am not convinced this Part of GUID value will always be unique, so be careful.

Answer 2

SELECT SUBSTRING(REPLACE(CONVERT(varchar, NEWID()), '-', ''), 1, 10)