MYSQL组\u CONCAT包含NULL

我使用此代码对设备进行分组，但当id_材质没有设备时，id_材质不会显示

select
material.id_material, 
material.mat_part_number, 
group_concat(distinct equipment.equipment_name order by equipment.equipment_name separator ', ') as equipment    
FROM material   
INNER JOIN equipment_list ON material.id_material=equipment_list.PKid_material INNER JOIN equipment ON equipment_list.PKid_equipment=equipment.id_equipment group by id_material;

我希望它看起来像这样

+-------------+----------------+
| id_material | equipment      |                                                             
+-------------+----------------+
|     1000001 | eq1            |         
|     1000002 | eq1, eq2       |
|     1000003 | eq3            |
|     1000004 |                |                           
+-------------+----------------+

但似乎只有这样

+-------------+----------------+
| id_material | equipment      |                                                             
+-------------+----------------+
|     1000001 | eq1            |         
|     1000002 | eq1, eq2       |
|     1000003 | eq3            |                        
+-------------+----------------+

---

我应该把空条件放在哪里

我刚刚修改了您的查询，这可能会对您有所帮助

SELECT 
  material.id_material, 
  material.mat_part_number, 
  GROUP_CONCAT(
    DISTINCT equipment.equipment_name 
    ORDER BY 
      equipment.equipment_name SEPARATOR ', '
  ) AS equipment 
FROM 
  material 
  LEFT JOIN equipment_list ON material.id_material = equipment_list.PKid_material 
  LEFT JOIN equipment ON equipment_list.PKid_equipment = equipment.id_equipment 
GROUP BY 
  id_material;

---

花点时间阅读帮助中心中的。堆栈溢出上的格式设置与其他站点不同。您的帖子越好看，其他人就越容易阅读和理解。请在末尾添加

设备“”

。很抱歉，我是个新手，仍然对代码的格式感到困惑：（你能告诉我应该在哪里学习吗？如果我把

拥有设备“”

放在末尾，没有设备名称的id\u材料不会显示。你需要将

内部连接设备列表

更改为

左连接设备列表