次數多行的值，MySQL的

Question

臺設備：

id device type_id device_status 
1  dev1  2  1   
2  dev2  2  2   
3  dev3  7  2   
4  dev5  9  3   

型號表：

model_id vendor_id model_name 
    1  3   name1   
    2  5   name2  
    3  7   name3   
    4  7   name4 

和查詢中查找此：

SELECT model_id, type_id, model_name, 
COUNT(type_id) AS numOfDevices 
FROM devices 
LEFT JOIN models ON models.model_id = devices.type_id 
WHERE device_status = 2 OR device_status = 3 
GROUP BY type_id 

什麼，我從得到該查詢是：

There are $numOfDevices $model_name items. 

這是好的，但有沒有一種方法可以在同一個查詢中僅使用device_status = 3對設備進行計數？

Answer 1

也許是這樣的：

SELECT model_id, type_id, model_name, 
SUM(CASE WHEN device_status=2 THEN 1 ELSE 0 END) AS device2, 
SUM(CASE WHEN device_status=3 THEN 1 ELSE 0 END) AS device3, 
SUM(CASE WHEN device_status IN (2,3) THEN 1 ELSE 0 END) AS device2device3 
FROM devices 
LEFT JOIN models ON models.model_id = devices.type_id 
WHERE device_status = 2 OR device_status = 3 
GROUP BY type_id