Question

编辑：对不起！我正在使用Microsoft SQL Server。

为了澄清，您可以拥有一个名为“x”的部门，其中包含一个工作列表，一个名为“y”的部门，其中包含不同的工作列表等。

我还需要使用＆gt; = ALL代替TOP 1或MAX，因为如果需要，我需要它返回多个值（如果job1有20名员工，job2有20名员工，他们都是最大值，他们应该都返回）。

在我的查询中，我正在努力找到最常见的职位标题和在此职位下工作的员工人数，这是在“研究与开发”部门下。我写的查询包含连接，以便能够返回必要的数据。

我遇到的问题是WHERE语句。 HAVING COUNT（JobTitle）＆gt; = ALL正在寻找在工作中工作的最多员工，但问题是我的WHERE声明说部门必须是'研发'，但是工作量最大的工作员工来自不同的部门，因此输出只产生列名而不产生其他任何内容。

我想重做查询，以便返回来自研发部门的员工人数最多的工作。

我知道这可能很简单，我是个菜鸟：3非常感谢你的帮助！

SELECT JobTitle, COUNT(JobTitle) AS JobTitleCount, Department
FROM HumanResources.Employee AS EMP JOIN 
     HumanResources.EmployeeDepartmentHistory AS HIST
     ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
     HumanResources.Department AS DEPT
     ON HIST.DepartmentID = DEPT.DepartmentID
WHERE Department = 'Research and Development'
GROUP BY JobTitle, Department
HAVING COUNT(JobTitle) >= ALL (
  SELECT COUNT(JobTitle) FROM HumanResources.Employee
  GROUP BY JobTitle 
)

Answer 1

如果您只想要一行，那么典型的方法是：

SELECT JobTitle, COUNT(*) AS JobTitleCount
FROM HumanResources.Employee AS EMP JOIN 
     HumanResources.EmployeeDepartmentHistory AS HIST
     ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
     HumanResources.Department AS DEPT
     ON HIST.DepartmentID = DEPT.DepartmentID
WHERE Department = 'Research and Development'
GROUP BY JobTitle
ORDER BY  COUNT(*) DESC
FETCH FIRST 1 ROW ONLY;

虽然FETCH FIRST 1 ROW ONLY是ANSI标准，但有些数据库会将其拼写为LIMIT甚至SELECT TOP (1)。

请注意，我从DEPARTMENT和SELECT中删除了GROUP BY。这似乎是多余的。

而且，如果我不得不猜测，由于历史表，您的查询会夸大结果。如果是这种情况，请询问另一个问题，并提供样本数据和所需结果。

编辑：

在SQL Server中，我建议使用窗口函数。要获得一个最高职位：

SELECT JobTitle, JobTitleCount
FROM (SELECT JobTitle, COUNT(*) AS JobTitleCount,
             ROW_NUMBER() OVER (ORDER BY COUNT(*) DESC) as seqnum
      FROM HumanResources.Employee AS EMP JOIN 
           HumanResources.EmployeeDepartmentHistory AS HIST
           ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
           HumanResources.Department AS DEPT
           ON HIST.DepartmentID = DEPT.DepartmentID
      WHERE Department = 'Research and Development'
      GROUP BY JobTitle
     ) j
WHERE seqnum = 1;

要获取所有此类标题，如果有重复项，请使用RANK()或DENSE_RANK()代替ROW_NUMBER()。

Answer 2

with employee_counts as (
    select
        hist.DepartmentID, emp.JobTitle, count(*) as cnt,
        case when dept.Department = 'Research and Development' then 1 else 0 end as is_rd,
    from HumanResources.Employee as emp
         inner join HumanResources.EmployeeDepartmentHistory as hist
             on hist.BusinessEntityID = emp.BusinessEntityID
         inner join HumanResources.Department as dept
             on dept.DepartmentID = hist.DepartmentID
    group by
        hist.DepartmentID, emp.JobTitle
)
select * from employee_counts
where is_rd = 1 and cnt = (
    select max(cnt) from employee_counts
    /* where is_rd = 1 */ -- ??
);

SQL查询 - 不确定如何修复逻辑错误

2 个答案: