Question

有人知道一个声明，它会从输出中删除这样的重复项吗？

DEPARTMENT_ID  DEPARTMENT_NAME                FULL_NAME               JOB_TITLE      
 50            Shipping                  Alana Walsh          Sales Representative
 50            Shipping                  Alana Walsh          Sales Representative  
 50            Shipping                  Winston Taylor       Sales Manager   
 50            Shipping                  Winston Taylor       Sales Manager
 60              IT                      Alexander Hunold     Sales Representative
 60              IT                      Alexander Hunold     Sales Representative

这是我到目前为止所拥有的：

select employees.department_id, departments.department_name, first_name || ' ' || last_name as full_name, job_title
from departments, employees, jobs
where employees.department_id = departments.department_id
and job_title like '%Sales%'
order by job_title, full_name;

Answer 1

您可以使用SELECT DISTINCT删除重复项。

select distinct employees.department_id, departments.department_name, first_name || ' ' || last_name as full_name, job_title
from departments, employees, jobs
where employees.department_id = departments.department_id
and job_title like '%Sales%'
order by job_title, full_name;

或者，您也可以在每列上使用GROUP BY

select employees.department_id, departments.department_name, first_name || ' ' || last_name as full_name, job_title
from departments, employees, jobs
where employees.department_id = departments.department_id
and job_title like '%Sales%'
group by employees.department_id, departments.department_name, first_name || ' ' || last_name as full_name, job_title
order by job_title, full_name;

看起来你错过了一份工作联盟？这可能是您的查询返回重复结果的原因。

我还建议你尽可能使用显式连接语法。

FROM departments
 INNER JOIN employees ON employees.department_id = departments.department_id

Answer 2

您可以使用DISTINCT作为Matt Busche指示。

然而，在许多情况下，人们错误地添加DISTINCT来掩盖他们缺少连接条件这一事实。在您的情况下，您将一起加入三个表 - departments，employees和jobs - 但您只有一个连接条件。因此，您正在与jobs表进行笛卡尔联接，这几乎肯定不是您想要的。 jobs表如何与其他两个表相关联？如果我们假设job_id和jobs表中都有employees，那么您需要类似

的内容

select employees.department_id, 
       departments.department_name, 
       first_name || ' ' || last_name as full_name, 
       job_title
  from departments, employees, jobs
 where employees.department_id = departments.department_id
   and jobs.job_id             = employees.job_id
   and job_title            like '%Sales%'
 order by job_title, full_name;

重复输出结果在oracle sql中

2 个答案: