how to know space used per column

I know I can use sp_spaceused to check space used per table.
However, how can I know space used per column?SELECT SUM(DATALENGTH(<column_name> )) should get you pretty close to that.
Jacco Schalkwijk
SQL Server MVP
"Guoqi Zheng" <no@.sorry.com> wrote in message
news:eMxBo4RBFHA.608@.TK2MSFTNGP15.phx.gbl...
>I know I can use sp_spaceused to check space used per table.
> However, how can I know space used per column?
>