Identity key on varchar column - T-SQL

Question

Hi there. I want to know if I can create an Identity (auto increment on a Varchar column. and how can I make it a primary key and create foreign key references on other table.

This is the code i have -

CREATE TABLE Questions(
    QuestionID int IDENTITY PRIMARY KEY, 
    QuestionNo as 'Q'+Cast(QuestionID as Varchar(10),       
    Question Varchar(200)
)

Is there a way I can make QuestionNo as Primary key and reference it in another table (say Answers (AnswerID, QuestionNo, AnswerText)?

Answer 1

This worked for me on SQL Server 2005:

CREATE TABLE Questions(
  QuestionID int IDENTITY NOT NULL, 
  QuestionNo as 'Q'+Cast(QuestionID as Varchar(10)) PERSISTED PRIMARY KEY, 
  Question Varchar(200)
)

The main part is that a computed column needs the PERSISTED keyword...

Answer 2

Not directly.

• use a computed column on an integer column (as per OMG Ponies answer)
• use a udf (SO1, SO2)

My question is: why? it will be slower than a straightforward number.