Sql 数多对多

我在

联系人

和

项目

之间有多对多的关联

contact:
+-----------------+--------------+------+-----+---------+----------------+
| Field           | Type         | Null | Key | Default | Extra          |
+-----------------+--------------+------+-----+---------+----------------+
| id              | int(11)      | NO   | PRI | NULL    | auto_increment |
+-----------------+--------------+------+-----+---------+----------------+

project:
+-------------------+--------------+------+-----+---------+----------------+
| Field             | Type         | Null | Key | Default | Extra          |
+-------------------+--------------+------+-----+---------+----------------+
| id                | int(11)      | NO   | PRI | NULL    | auto_increment |
+-------------------+--------------+------+-----+---------+----------------+

project_contact:
+---------------+---------+------+-----+---------+-------+
| Field         | Type    | Null | Key | Default | Extra |
+---------------+---------+------+-----+---------+-------+
| project_id    | int(11) | NO   | PRI | NULL    |       |
| contact_id    | int(11) | NO   | PRI | NULL    |       |
+---------------+---------+------+-----+---------+-------+

我想计算有多少联系人与无项目、一个项目或多个项目关联。如果我能在一个查询中得到它，那将是非常棒的，如果不能，三个不同的查询也可以

PS：我正在使用HQL，但是我在将SQL转换为HQL时不会有问题

谢谢

我称之为“直方图直方图”查询。它基本上是聚合之上的聚合：

select NumProjects, count(*) as NumContacts
from (select c.id, count(pc.contact_id) as NumProjects
      from contacts c left join
           project_contacts pc
           on pc.contact_id = c.id
      group by c.id
     ) c
group by NumProjects
order by NumProjects;

我称之为“直方图”查询。它基本上是聚合之上的聚合：

select NumProjects, count(*) as NumContacts
from (select c.id, count(pc.contact_id) as NumProjects
      from contacts c left join
           project_contacts pc
           on pc.contact_id = c.id
      group by c.id
     ) c
group by NumProjects
order by NumProjects;

---

您可以使用HQL或条件查询。假设域模型与此类似

class Project {
    static hasMany = [contact: Contact]
}

class Contact {
    static hasMany = [project: Project]
    static belongsTo = Project
}

HQL 条件查询

---

您可以使用HQL或条件查询。假设域模型与此类似

class Project {
    static hasMany = [contact: Contact]
}

class Contact {
    static hasMany = [project: Project]
    static belongsTo = Project
}

HQL 条件查询

---

不幸的是，联系人表中有一组

ProjectContact

元素，而不是一组项目，但谢谢您！不幸的是，联系人表中有一组

ProjectContact

元素，而不是一组项目，但谢谢您！