1、
as后面不加单引号或双引号====>MySql和Oracle都可以运行，例如：
SELECT aaa AS 啊啊啊,bbb AS 不不不,ccc AS 错错错 FROM table_name
2、
as后面加单引号====>MySql可以运行，Oracle运行会报错，例如：
SELECT aaa AS '啊啊啊',bbb AS '不不不',ccc AS '错错错' FROM table_name
3、
as后面加双引号====>Oracle可以运行，MySql运行会报错，例如：
SELECT aaa AS "啊啊啊",bbb AS "不不不",ccc AS "错错错" FROM table_name
