Question

尽管在PostgreSQL中工作，为什么不选择在Oracle中工作（第三个总和应该是相同的：从员工中选择总和（薪水））？：

select e1.employee_id, e1.department_id, e1.manager_id, e1.salary,
sum(e2.salary), sum(e3.salary)
from employees e1, employees e2, employees e3
where e1.department_id=e2.department_id
group by e1.employee_id, e1.department_id, e1.manager_id, e1.salary  
order by 1,2;

它适用于PostgreSQL，但不适用于此。在Oracle中，只有一个副本e2没有任何约束（当e1是原始表并按主键分组时）：

 select e1.employee_id, e1.department_id, e1.manager_id, e1.salary,
    sum(e2.salary)
    from employees e1, employees e2
    where e1.department_id=e2.department_id
    group by e1.employee_id, e1.department_id, e1.manager_id, e1.salary  
    order by 1,2;

甚至没有作为第一张表的每条记录的总和（这里没有约束）：

 select e1.employee_id, e1.department_id, e1.manager_id, e1.salary,
    sum(e2.salary)
    from employees e1, employees e2
    group by e1.employee_id, e1.department_id, e1.manager_id, e1.salary  
    order by 1,2;

当然，我知道其他选择，例如：

select employee_id, department_id, manager_id, salary, 
sum(salary) over (partition by department_id) as suma,
sum(salary) over ()
from employees order by 2,3;

或使用子选择：

select employee_id, department_id, manager_id, salary, 
(select sum(e2.salary) from employees e2
where e2.department_id=e1.department_id) as suma1,
(select sum(e2.salary) from employees e2) as suma2
from employees e1 order by 1,2;

您是否知道在Oracle中执行多个表副本的方法？

Answer 1

在您的第一个查询中，您创建了一个完整的笛卡尔积，因为您没有设置任何约束来匹配表

之后有2个表副本

1 个答案: