单行子查询返回多行

admin

单行子查询返回多行

sql

我需要有关oracle
sql的帮助。问题：我有2个表的员工和部门。我从一个查询中获得了部门的平均薪水，我想用它来查看有多少员工比部门的平均薪水更高。到目前为止，我已经知道了。

此查询返回部门的平均值：

select ROUND(AVG(Salary), 2) Dept_avg_sal
 from employee, department
 where department.department_id = employee.department_id
 group by department_name

我想做的是：

select employee_name,
       salary,
       d.department_name
from   employee e,
       department d
where  salary > (select ROUND(AVG(Salary), 2) Dept_avg_sal
                 from   employee,
                        department
                 where  department.department_id = employee.department_id
                 group  by department_name)

我得到的错误是：01427。00000-“单行子查询返回多个行”

我知道同一部门的2名员工比平均收入更高，我认为这是造成此问题的原因。

EMPLOYEE_NAME       - SALARY -                -DEPARTMENT_NAME-      DEPT_AVG_SAL           
-------------------- ---------------------- -------------------- ------------ 
FISHER              - 3000.00  -              SALES      -          2500.00                   
JONES          -      3000.00               - ACCOUNTING         -  2750.00                   
KING             -    5000.00           -     EXECUTIVE     -       4500.00                   
**SCOTT           -     2500.00           -     IT             -      2100.00                   
SMITH           -     2900.00          -      IT     -              2100.00**                   
WILSON           -    3000.00          -      RESEARCH      -       2633.33

任何帮助将非常感激。

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2021-07-01

共1个答案

admin

您的初始查询缺少外部查询上的任何连接条件以及内部查询中的任何关联条件，这些条件会将其限制为仅关注部门的行。另外一般你不想group by name为想必id是主键。

解决这些问题以修复相关的子查询可以

SELECT e.employee_name,
       e.salary,
       d.department_name
FROM   employee e
       JOIN department d
         ON d.department_id = e.department_id
WHERE  e.salary > (SELECT ROUND(AVG(Salary), 2) Dept_avg_sal
                   FROM   employee e2
                   WHERE  e2.department_id = e.department_id)

但是，您可能会发现放弃标量相关子查询并替换为派生表会更好。

SELECT e.employee_name,
       e.salary,
       d.department_name
FROM   employee e
       JOIN department d
         ON d.department_id = e.department_id
       JOIN (SELECT ROUND(AVG(Salary), 2) Dept_avg_sal,
                    department_id
             FROM   employee
             GROUP  BY department_id) e2
         ON e2.department_id = e.department_id
            AND e.salary > e2.Dept_avg_sal

对于Oracle，以下内容也应该有效

SELECT employee_name,
       salary,
       d.department_name
FROM   (SELECT employee_name,
               salary,
               d.department_name,
               AVG(Salary) OVER (PARTITION BY e.department_id) AS AvgSalary
        FROM   employee e
               JOIN department d
                 ON d.department_id = e.department_id)
WHERE  salary > AvgSalary

2021-07-01