在MYSQL中显示3列的多个选择，值为NULL

Question

我有这两张桌子：

瞳孔：

id_pupil
name
surname
email
user
pass
level
class

事件：

id_incidents
date
time
type_incident(miss, delay or attitude)
comments
id_pupil
id_user
subject
id_trimester

我想得到这个：

我写这个：

select pupils.id_pupil, name, surname, count(type_incident) as misses 
from pupils left join incidents using (id_pupil) 
where type_incident='miss' and level=1 and class='B' and id_trimester=1 
group by id_pupil

我得到了每个学生未命中的专栏。但是，我没有得到空值，因为我想得到0个未命中的学生。

同样的延迟和态度：

select pupils.id_pupil, name, surname, count(type_incident) as misses 
from pupils left join incidents using (id_pupil) 
where type_incident='delay' and level=1 and class='B' and id_trimester=1 
group by id_pupil

select pupils.id_pupil, name, surname, count(type_incident) as misses 
from pupils left join incidents using (id_pupil) 
where type_incident='attitude' and level=1 and class='B' and id_trimester=1 
group by id_pupil

我希望所有人都在图片中描述的同一张表中。

谢谢！

Answer 1

我认为juergen的答案会比我的更好，因为代码更具可读性，但由于我已经输入了我的内容，我会继续发布另一种方法来实现相同的结果：我原来的两个建议是添加{ {1}}和name到您的GROUP BY语句;另外，将条件surname从WHERE上移到你的LEFT JOIN中，如下所示：

and id_trimester=1

Answer 2

将条件放在sum()中。它总结了您的条件成立的次数（1）

select pupils.id_pupil, name, surname, 
       sum(type_incident='miss' and level=1 and class='B' and id_trimester=1) as misses,
       sum(type_incident='delay' and level=1 and class='B' and id_trimester=1) as delays,
       sum(type_incident='attitude' and level=1 and class='B' and id_trimester=1) as attitudes
from pupils 
left join incidents using (id_pupil) 
group by id_pupil, name, surname

SQLFiddle demo

Answer 3

SELECT CONCAT(p.name, ' ', p.surname) AS Pupil, t1.misses, t2.delays, t3.attitude
FROM pupils AS p
LEFT JOIN (SELECT COUNT(*) AS misses FROM id_incidents WHERE type_incident = 'miss' and level=1 and class='B' and id_trimester=1) AS t1 ON (t1.id_user = p.id_pupil)
LEFT JOIN (SELECT COUNT(*) AS delays FROM id_incidents WHERE type_incident = 'delay' and level=1 and class='B' and id_trimester=1) AS t2 ON (t2.id_user = p.id_pupil)
LEFT JOIN (SELECT COUNT(*) AS attitude FROM id_incidents WHERE type_incident = 'attitude' and level=1 and class='B' and id_trimester=1) AS t3 ON (t3.id_user = p.id_pupil)