Sql_Server中如何判斷表中某列是否存在

/*判斷表AA中是否存在AA_ID這一列，如果不存在，則新增*/  
IF NOT EXISTS (SELECT 1  FROM syscolumns INNER JOIN sysobjects ON sysobjects.id = syscolumns.id   
        WHERE syscolumns.name = 'AA_ID' AND sysobjects.name = 'AA')  
ALTER TABLE AA ADD AA_ID VARCHAR(30) NULL   
GO