Question

如何在我的SQL脚本中将子查询添加为列？

e.g。

Select emp_no, name,gender ,
    (select department_name from departments where employees.emp_no = departments.emp_no)
from employees

PS：我正在使用oracle 8

Answer 1

按照语义，我理解的是，您希望员工的部门名称与他/她的其他信息一起显示。我建议你做一个加入：

Select emp_no, name, gender, department_name
from employees emp, departments dept
where emp.emp_no = dept.emp_no;

Answer 2

看起来听起来合理，我建议清理一些（可能的拼写错误）：在“性别”之后添加一个逗号并声明表名，同时设置子查询别名

Select employees.emp_no, employees.name, employees.gender,  
    (select departments.department_name from departments where employees.emp_no = departments.emp_no) as dept_name
from employees

或者，如果其他数据可行，那么一个好的连接也会起作用：

Select employees.emp_no, employees.name, employees.gender,  departments.department_name
from employees
inner join departments on employees.emp_no = departments.emp_no

Answer 3

left join是最佳做法，应该在性能上更快：

Select e.emp_no, e.name, e.gender , d.department_name
from employees e left join departments d on e.emp_no = d.emp_no;

Answer 4

你似乎在性别之后缺少逗号。

Select emp_no, name,gender ,
(select department_name from departments     where employees.emp_no = departments.emp_no) as dept_name from employees

Answer 5

以下是您的需求。只是在性别后添加了一个逗号。此子查询也需要为每个结果只返回一行，否则将看到错误。

Select emp_no, name,gender, 
    (select department_name from departments where employees.emp_no = departments.emp_no)
from employees

Answer 6

此查询是您的答案，但只有在我们使用多个列而不是重新发送错误时才会提到一列时，它才会起作用。

"Select employee_id,first_name,
    (select department_name,manager_id from departments where employees.department_id = departments.department_id) as new_column
from employees;"

Answer 7

你可以试试这个：

SELECT em.emp_no, em."name",em.gender , (SELECT的不同 dp.department_name FROM departments dp WHERE em.emp_no = dp.emp_no) my_sub FROM employees em

如何在SQL中将子查询添加为列

7 个答案: