How to change a normal column to "computed" column

I ha开发者_运维技巧ve a table in MSSQL server 2008. I would like to change one of the column in that table to computed column. Could somebody tell me how do I do that ?

Preserve the old data:

EXEC sp_rename 'MyTable.OldCol', 'RenamedOldCol', 'COLUMN';

Add computed column

ALTER TABLE MyTable ADD ComputedCol AS (some expression);

Then, when you're happy

ALTER TABLE MyTable DROP COLUMN RenamedOldCol;