The PK of a table

Here is the code to get the PK of a table.

CREATE PROCEDURE GetTablePK(
@TableName Varchar(20) = NULL
)
AS
BEGIN
select [name] from syscolumns where
   [id] in (select [id]
            from sysobjects
            where [name] = @TableName) and
   colid in (select SIK.colid
             from
                sysindexkeys SIK join sysobjects SO on
                SIK.[id] = SO.[id] 
             where
                SIK.indid = 1 and
                SO.[name] = @TableName)
END

we use the system table sys.sysindexkeys that contains information about the keys or columns in an index of the database.