Add a column to a table with a default value equal to the value of an existing column

Question

How to add a column to a SQL Server table with a default value that is equal to value of an existing column?

I tried this T-SQL statement:

ALTER TABL         


        

Answer 1

I don't like them very much but here is how you could do this with an AFTER INSERT trigger:

CREATE TRIGGER TableX_AfterInsert_TRG 
  ON TableX 
AFTER INSERT
AS
  UPDATE TableX AS t
  SET t.newcolumn = t.oldcolumn
  FROM Inserted AS i
  WHERE t.PK = i.PK ;              -- where PK is the PRIMARY KEY of the table