使用 MySQL 为交叉表拉入第二个值

Question

我有以下查询...

SELECT COUNT(Department) as DeptCount, Survey.Department, Department.DepartmentName 
FROM Survey JOIN Department ON Survey.Department = Department.DeptID 
Where SurveyCompleted is not null GROUP BY DEPARTMENT ORDER BY Department;

唯一的问题是我用来计数的字段 "Department" 并不总是输入值（出于多种原因）。我可以使用另一个字段 Employee.DepartmentId，但我不确定如果我使用内联 IF 或类似结构如何创建相同的效果。

基本上我想看到的输出是：

DeptCount    Department    DepartmentName
43           2             Department1
68           9             Department2
83           13            Department3

现在我得到一个额外的行作为第一个结果

DeptCount    Department    DepartmentName
93           0             <blank>
43           2             Department1
68           9             Department2
83           13            Department3

如有任何帮助，我们将不胜感激。

谢谢。

Answer 1

如果你尝试这个会发生什么？通过使连接成为左连接，我们从 Survey 中获取所有记录，并从 Department 中获取任何匹配记录。然后我们可以聚合它们。

SELECT COUNT(Department) as DeptCount, coalesce(Survey.Department, 0)
, Department.DepartmentName 
FROM Survey 
left JOIN Department ON Survey.Department = Department.DeptID
Where SurveyCompleted is not null 
GROUP BY DEPARTMENT ORDER BY Department;

顺便说一下，group by 会自动排序，所以如果您要分组，则不需要 order by。

Answer 2

试试这个

SELECT COUNT(Department) as DeptCount, Survey.Department, Department.DepartmentName 
FROM Survey JOIN Department ON Survey.Department = Department.DeptID 
Where SurveyCompleted is not null and Survey.Department is not null and Survey.Department <> ''   
GROUP BY DEPARTMENT   
ORDER BY Department;

Answer 3

看来我想把它弄得太复杂了。

我需要做的就是命名从条件运算符创建的结果。然后我可以按该值分组......它有效（或似乎有效）。

这是我的查询结果：

SELECT COUNT(Department) as DeptCount, 
  IF(Survey.Department=0, Employee.DepartmentId, Survey.Department) As MyDept, 
  Department.DepartmentName 
FROM Survey JOIN Department ON Survey.Department = Department.DeptID
  JOIN Employee ON EmployeeId = Employee.Id
WHERE SurveyCompleted is not null
GROUP BY MyDept;

使用 MySQL 为交叉表拉入第二个值

Pulling in a second value for a Cross Tab with MySQL

mysql

conditional-operator