如何包含MySQL COUNT爲0的行？

Question

我使用下面的查詢返回如下結果：

SELECT subnets.subnet_id , INET_NTOA( subnets.address) AS inet_address, subnet_masks.hosts, COUNT(addresses.STATUS) AS status_count 
FROM subnets 
LEFT JOIN subnet_masks ON subnets.mask_id = subnet_masks.mask_id 
LEFT JOIN addresses ON subnets.subnet_id = addresses.subnet_id 
WHERE addresses.status = 'allocated' 
GROUP BY subnet_id  
ORDER BY subnets.address 



subnet_id inet_address hosts status_count 
91   10.10.10.0  65534 3 
71   192.168.1.0  254  6 
90   192.168.10.0 254  1 

但是我希望它返回太指望0行，就像這樣：

subnet_id inet_address hosts status_count 
91   10.10.10.0  65534 3 
76   172.128.0.0  254  0 
71   192.168.1.0  254  6 
90   192.168.10.0 254  1 

，我讀了它可能是我的JOIN問題，所以我嘗試了許多不同的方法，並得到相同的結果。有誰知道我做錯了什麼？

Answer 1

你WHERE子句過濾掉的記錄......它移動到你的LEFT JOIN來解決問題：

SELECT subnets.subnet_id , INET_NTOA( subnets.address) AS inet_address, subnet_masks.hosts, COUNT(addresses.STATUS) AS status_count 
FROM subnets 
LEFT JOIN subnet_masks ON subnets.mask_id = subnet_masks.mask_id 
LEFT JOIN addresses ON subnets.subnet_id = addresses.subnet_id AND addresses.status = 'allocated' 
GROUP BY subnet_id  
ORDER BY subnets.address 

Answer 2

試試這個：

SELECT subnets.subnet_id , INET_NTOA( subnets.address) AS inet_address, 
    subnet_masks.hosts, COUNT(addresses.STATUS) AS status_count 
FROM subnets 
LEFT JOIN subnet_masks ON subnets.mask_id = subnet_masks.mask_id 
LEFT JOIN addresses ON subnets.subnet_id = addresses.subnet_id 
    and addresses.status = 'allocated' 
GROUP BY subnet_id  
ORDER BY subnets.address 

Answer 3

你的where子句指定address.status =「分配」，但與status_count等於0的行沒有地址，因此不能有這樣的狀態。

Answer 4

你的左連接錯了，它應該是這樣的

SELECT subnets.subnet_id , INET_NTOA( subnets.address) AS inet_address, subnet_masks.hosts, COUNT(addresses.STATUS) AS status_count 
FROM subnets 
LEFT JOIN subnet_masks ON subnets.mask_id = subnet_masks.mask_id 
LEFT JOIN addresses ON subnets.subnet_id = addresses.subnet_id AND addresses.status = allocated' 
GROUP BY subnet_id  
ORDER BY subnets.address