Sql_Server中怎样推断表中某列是否存在

/*推断表AA中是否存在AA_ID这一列。假设不存在，则新增*/
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