错误是“组函数嵌套太深”？答案

【问题标题】：ERROR is "group function is nested too deeply"?错误是“组函数嵌套太深”？
【发布时间】：2017-10-19 01:46:08
【问题描述】：

试图显示学生人数最少的部门的名称。

【问题讨论】：

您的查询是无意义的。所以请参阅meta.stackoverflow.com/questions/333952/…

【解决方案1】：

试试这样的：

SELECT TOP 1 department_name, count(*) AS number_of_students
FROM department natural join student
GROUP BY department_name
ORDER BY number_of_students

它将为您提供按学生人数排序的部门列表。通过TOP 1 仅选择第一行，您只会获得学生人数最少的部门。

【讨论】：

只需要显示部门名称，并且可以有多个具有相同最小值的行。
TOP 是 MSSQL 语法而不是 MySQL 语法，所以你的答案不正确

【解决方案2】：

是这样的吗？

SELECT 
T1.department_name, COUNT(T2.department_id) totalCount
FROM department T1
LEFT JOIN student T2
ON T1.department_id = T2.department_id
GROUP BY T2.department_id
HAVING COUNT(T2.department_id) =
(
  SELECT  
  COUNT(T2.department_id) totalCount
  FROM department T1
  LEFT JOIN student T2
  ON T1.department_id = T2.department_id
  GROUP BY T2.department_id
  ORDER BY totalCount ASC
  LIMIT 1
)

SQLFIDDLE DEMO

【讨论】：