为什么这个查询使用UNION ALL不工作

Question

我有以下查询：

SELECT a.status, count(a.status) FROM 
(SELECT 'Delivered' AS status 
UNION ALL SELECT 'Buffered' 
UNION ALL SELECT 'Not Delivered' 
UNION ALL SELECT 'Not Reported') a 
LEFT JOIN 
bulk_sms_numbers 
ON a.status = bulk_sms_numbers.delivery_status 
WHERE bulk_sms_id = 52 
GROUP BY a.status; 

，并得到以下结果：

+-----------+-----------------+ 
| status | count(a.status) | 
+-----------+-----------------+ 
| Buffered |    10 | 
| Delivered |   3200 | 
+-----------+-----------------+ 

我想要的结果集包含所有的候选条件中的状态列union all查询

输出我需要的示例。

+---------------+-----------------+ 
| status  | count(a.status) | 
+---------------+-----------------+ 
| Buffered  |    10 | 
| Delivered  |   3200 | 
| Not Delieverd |    0 | 
| Not Reported |    0 | 
+---------------+-----------------+ 

我使用MySQL

Answer 1

移动从WHERE子句条件为ON，因此筛选将发生，而加入，而不是最终结果列表上。

SELECT a.status, count(a.status) 
FROM 
    (
     SELECT 'Delivered' AS status 
     UNION ALL SELECT 'Buffered' 
     UNION ALL SELECT 'Not Delivered' 
     UNION ALL SELECT 'Not Reported' 
    ) a 
    LEFT JOIN bulk_sms_numbers 
     ON a.status = bulk_sms_numbers.delivery_status AND 
      bulk_sms_id = 52 
GROUP BY a.status; 

• SQLFiddle Demo Example

Answer 2

尝试也给列名于一切，改变ON是有条件的

SELECT a.status, count(a.status) FROM 
(SELECT 'Delivered' AS status 
UNION ALL SELECT 'Buffered' As status 
UNION ALL SELECT 'Not Delivered' as status 
UNION ALL SELECT 'Not Reported' as status) a 
LEFT JOIN 
bulk_sms_numbers 
ON a.status = bulk_sms_numbers.delivery_status 
AND bulk_sms_id = 52 
GROUP BY a.status; 

Answer 3

尝试移动WHERE条件到ON子句，并使用一个外加入。

SELECT a.status, count(a.status) FROM 
(SELECT 'Delivered' AS status 
UNION ALL SELECT 'Buffered' 
UNION ALL SELECT 'Not Delivered' 
UNION ALL SELECT 'Not Reported') a 
LEFT OUTER JOIN 
bulk_sms_numbers 
ON a.status = bulk_sms_numbers.delivery_status 
AND bulk_sms_id = 52 
GROUP BY a.status; 

Answer 4

我最终使用的查询是这样的：

SELECT cnt, IFNULL(delivery_status, 'Not Reported') delivery_status FROM (
    SELECT delivery_status, count(delivery_status) cnt FROM bulk_sms_numbers WHERE bulk_sms_id = 52 GROUP BY delivery_status 
) x 

，然后在PHP我的所有状态设置默认值0

$data = $db->fetchAll($q, array($aid, $reference)); 

$statuses = array(
    'Buffered' => 0, 
    'Delivered' => 0, 
    'Not Delivered' => 0, 
    'Not Reported' => 0, 
); 

foreach ($data as $value) { 
    $statuses[$value['delivery_status']] = $value['cnt']; 
} 

Althought这样做解决了我的问题，是不是我的问题的答案。 我想找到一个纯粹的SQL答案。