oracle -2

• 处理空值排序：select ename,sal,comm from emp order by comm nulls last; select ename,sal,comm from emp order by comm nulls first;   
• 根据数据项的键来排序：查看表结构：SELECT column_name, data_type FROM user_tab_columns WHERE table_name='DEPT'; 如果JOB是‘SALESMAN’，要根据COMM来怕pauxu.fouze，根据SAL排序。select ename, sal,job,comm from emp order by case when job='SALESMAN' then comm end;