How do you add a computed column to a Table?

Question

How can I add a computed column to a table that already exists? S.O. has Computed Column Help - TSQL but no information about adding them.

Solution

The syntax I was looking for is:

alter table TABLE_NAME
add [column_name] as (**COLUMN-SQL**)

Comments

[David Knight]

alter table TABLE_NAME add [column_name] as (**COLUMN-SQL**)

[veeresh yh]

EX: alter table TABLE_NAME add [double_count] as (count * 2)

[Sal]

To create a persisted column (calculated when the data is inserted) you can add the Persisted keyword: alter table TABLE_NAME add [column_name] as (COLUMN-SQL) PERSISTED

[enigma6205]

THis does now work when adding Row_Number column. ALTER TABLE MYDB.[dbo].[Table1] ADD Rn INT NOT NULL AS (ROW_NUMBER() OVER (PARTITION BY [MyColumn] ORDER BY [MyColumn]));

[Chris Pfohl]

I imagine that's a result of using a windowing function in a calculated column.