Question

SELECT department_name, cou  FROM 
(
    SELECT department_name, count(student_id) AS cou
    FROM department d NATURAL JOIN student s
    GROUP BY department_name
)
GROUP BY department_name HAVING cou=max(cou);

Answer 1

首先关闭 - 避免自然加入。这很危险。谷歌的原因。您收到的消息是因为您有OUTER选择的GROUP BY，但您在select子句中没有聚合函数。

看起来你可能完全失去外部选择并将HAVING子句放在内部选择上。

Answer 2

SELECT * FROM (
SELECT department_name, count(student_id) AS cou
  FROM department d 
  JOIN student s USING (student_id)
GROUP BY department_name
ORDER BY count(student_id) DESC )
WHERE rownum = 1

我收到错误ORA-00979。指出错误

2 个答案: