Question

当我在sql中编写此查询时显示错误（ORA-00998：必须使用列别名命名此表达式）

    create or replace view vw_salary as select dname ,
 (select count(*)  from employee where dno=department.dnumber) from department;

Answer 1

视图中的列需要具有名称。因此，在子查询后需要as：

create or replace view vw_salary as
    select dname,
           (select count(*) from employee e where e.dno = d.dnumber
           ) as NumEmployees
    from department d;

我强烈建议您使用表别名和限定列名（即使用表别名）。对于相关子查询来说，特别很重要，因为它很容易出错并且难以调试。

我还注意到该视图名为vw_salary，但没有工资信息。

Answer 2

select department.dname, count(employee.dno) as empCount 
  from department 
  left join employee 
         on employee.dno = department.dnumber 
 group by department.dname

我认为这比你当前的格式更有效

Answer 3

这意味着您需要为计数表达式命名...尝试以下操作，您可以更改＆＃34; TheCount＆＃34;您要使用的任何名称。

    create or replace view vw_salary as select dname ,
 (select count(*) AS TheCount from employee where dno=department.dnumber) from department;

如何在SQL plus中使用别名列

3 个答案: