ocp 051 第64题，有关order by 的试验

原题两个sql如下：

SQL>SELECT DISTINCT promo_category   to_char(promo_cost)"code"    

FROM promotions    

ORDER BY code;

SQL>SELECT DISTINCT promo_category   promo_cost "code"    

FROM promotions    

ORDER BY 1;

经过试验得到：

SELECT distinct ename || to_char(sal) "sl" from emp ORDER BY sl;----失败

SELECT distinct ename || to_char(sal) "sl" from emp ORDER BY 1;----可以成功

SELECT distinct ename || to_char(sal) sl from emp ORDER BY sl;-----可以成功

select ename AS "ea" from emp ORDER BY "ea";--------可以成功。

 

结论为：希望使用小写为列的别名，并且希望使用此别名排序时，必须和在命名别名时一样，在order by 中带上双引号.