SQL Server 2017

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CREATE TABLE Correspondence (ID int IDENTITY (1,1) NOT NULL, Type VARCHAR(100));
INSERT INTO Correspondence (Type) VALUES
  ('letter'), ('email'), ('User Note'), ('anything');
4 rows affected

ALTER TABLE Correspondence ADD TypeCode AS 
CASE [Type]
  WHEN 'letter' THEN 1
  WHEN 'email' THEN 2
  WHEN 'User Note' THEN 3
  ELSE 4
END;
SELECT * FROM Correspondence;


ID
Type
TypeCode


1
letter
1

2
email
2

3
User Note
3

4
anything
4