ORA-00998: must name this expression with a column alias

问题描述：创建视图时报错ORA-00998，如下所示：
SQL> create view v_emp80
2 as select employee_id,first_name || ' ' || last_name,salary,department_id
3 from employees
4 where department_id=80;

as select employee_id,first_name || ' ' || last_name,salary,department_id
*
ERROR at line 2:
ORA-00998: must name this expression with a column alias

异常原因：创建视图时，表达式需要别名，才能作为视图的列名，否则会报错.
添加别名后成功创建视图.
SQL> create view v_emp80
2 as select employee_id,first_name || ' ' || last_name name,salary,department_id
3 from employees
4 where department_id=80;

View created.