if (not exists (select name from syscolumns where id = object_id('Pub_Subject') and name = 'GradeGuid'))   
    Begin

    ALTER TABLE Pub_Subject ADD
    GradeGuid nvarchar(64)

    EXEC sys.sp_addextendedproperty @name=N'MS_Description', @value=N'ËùÊôÄ꼶
type:selectbox
fk_table:Pub_Grade
' ,@level0type=N'SCHEMA', @level0name=N'dbo', @level1type=N'TABLE', @level1name=N'Pub_Subject', @level2type=N'COLUMN', @level2name=N'GradeGuid'

    End