MYSQL GROUP_CONCAT包含NULL

Question

我使用此代码对设备进行分组，但是当id_material没有设备时，id_material不会显示。

DataSet

我希望它看起来像这样

DataTable

但它只会出现

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;

我应该在哪里放置NULL条件？

Answer 1

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;