我有两个表:
project (id, name)
list (id, name, project_id)
我想将每个项目和列表号都放入该项目。
我尝试过:
SELECT project.id, project.name, COUNT(list.id) AS list_count
FROM project
INNER JOIN list ON (list.project_id = project.id)
GROUP BY project.id DESC
但是我只得到有列表的项目。
如果该项目没有列表,我不会得到...
如果COUNT(list_id)= 0,我希望list_count = 0,我该怎么办?
答案 0 :(得分:5)
使用左联接代替内联接
SELECT project.id, project.name, COUNT(list.id) AS list_count
FROM project
Left JOIN list ON (list.project_id = project.id)
GROUP BY project.id DESC