MySQL的返回行有了零計數

Question

表佈局

reject_data

+-----------+-----------------+------------------+---------------+ 
| reject_id | reject_location | reject_equipment | reject_time | 
+-----------+-----------------+------------------+---------------+ 
| 1   | 7    | 6    | 1326795921000 | 
+-----------+-----------------+------------------+---------------+ 
| 2   | 7    | 1    | 1326796641000 | 
+-----------+-----------------+------------------+---------------+ 
| 3   | 7    | 6    | 1326799521000 | 
+-----------+-----------------+------------------+---------------+ 
| 4   | 6    | 5    | 1326800781000 | 
+-----------+-----------------+------------------+---------------+ 
| 5   | 7    | 3    | 1326802281000 | 
+-----------+-----------------+------------------+---------------+ 
| 6   | 7    | 4    | 1326802941000 | 
+-----------+-----------------+------------------+---------------+ 
| 7   | 7    | 1    | 1326814161000 | 
+-----------+-----------------+------------------+---------------+ 
| 8   | 6    | 2    | 1328026700000 | 
+-----------+-----------------+------------------+---------------+ 

設備

+--------------+------------------+ 
| equipment_id | equipment_string | 
+--------------+------------------+ 
| 1   | Microdoser  | 
+--------------+------------------+ 
| 2   | Monoblock  | 
+--------------+------------------+ 
| 3   | Valve Magnet  | 
+--------------+------------------+ 
| 4   | Checkweigher  | 
+--------------+------------------+ 
| 5   | Microleak  | 
+--------------+------------------+ 
| 6   | Capper   | 
+--------------+------------------+ 

查詢

SELECT equipment_string AS eqpt, COUNT(reject_id) AS cnt 
FROM reject_data 
RIGHT OUTER JOIN equipment ON (reject_equipment = equipment_id) 
WHERE reject_location IN (1,2,7) AND equipment_id IN (1,2,3,4,5,6) AND reject_time BETWEEN 1329479810000 AND 1329483410000 
GROUP BY equipment_id 
ORDER BY cnt DESC 

問題

如何更改我的查詢以便它還返回零計數的設備？很堅持:(

感謝您的幫助

注：動態變量填充在正常

Answer 1

WHERE子句在JOIN之後進行篩選，所以它會過濾掉任何記錄重新JOIN失敗（因爲reject_location IN (1,2,7)將不適用於那些）。您需要這些限制移動到ON條款：

SELECT equipment_string AS eqpt, COUNT(reject_id) AS cnt 
FROM reject_data 
RIGHT OUTER JOIN equipment 
     ON reject_equipment = equipment_id 
     AND reject_location IN (1,2,7) 
     AND reject_time BETWEEN 1329479810000 AND 1329483410000 
WHERE equipment_id IN (1,2,3,4,5,6) 
GROUP BY equipment_id 
ORDER BY cnt DESC 

在這種情況下，另一種方法，您可能發現更清晰，是使用一個子查詢，而不是加入：

SELECT equipment_string AS eqpt, 
     (SELECT COUNT(1) 
      FROM reject_data 
      WHERE reject_equipment = equipment_id 
      AND reject_location IN (1,2,7) 
      AND reject_time BETWEEN 1329479810000 AND 1329483410000 
     ) AS cnt 
    FROM equipment 
WHERE equipment_id IN (1,2,3,4,5,6) 
ORDER BY cnt DESC 

Answer 2

SELECT 
    e.equipment_string AS eqpt, 
    COUNT(reject_id) AS cnt 

FROM equipment AS e 

LEFT JOIN reject_data AS rd 
    ON rd.reject_equipment = e.equipment_id 
    AND rd.reject_location IN (1,2,7) 
    AND rd.reject_time BETWEEN 1329479810000 AND 1329483410000 

WHERE e.equipment_id IN (1,2,3,4,5,6) 

GROUP BY e.equipment_id 
ORDER BY cnt DESC 

通過限制你減少行的數量MySQL需要的連接標準。檢索