试图加入两个表,并计算一个部门的评论数量

Question

在尝试获取每个部门发表的评论总数时,我的sql无法正常工作.

select * from departments d
  COUNT( comments.department_id ) AS total_comments
FROM
  d
LEFT JOIN
  comments c
ON
  ( d.id = c.department_id )
GROUP BY
  d.id, d.title

comments.department_id = departments.id

更新:我忽略了提到我想以这种方式显示结果:departments.title(total_comments)

示例:维护(4)

已解决:需要将其分组为d.title,现在GROUP BY是d.id,d.title

Answer 1

SELECT departmentID, COUNT(*)
FROM COMMENTS
GROUP BY departmentID

如果你需要没有评论的部门:

SELECT d.DepartmentID, Count(c.DepartmentID)
FROM Departments d
LEFT JOIN Comments c on d.departmentid = c.departmentid
GROUP BY d.DepartmentID