0

2つの異なるデータベースに2つのテーブルがあります：

db1.table1 

+--------------+--------------------------+
| Username     | Message                  |
+--------------+--------------------------+
| jamesbond    | I need some help         |
| jamesbond    | I need some help         |
| jamesbond    | I need some help         |
| jamesbond    | Mission accomplished     |
+--------------+--------------------------+

db2.table2 

+--------------------------+--------------+
| Message                  | Status       |
+--------------------------+--------------+
| I need some help         | Ok           |
| I need some help         | Ok           |
| I need some help         | Bad          |
+--------------------------+--------------+

このSQL構文を使用してこれらのテーブルを「INNERJOIN」すると、次のようになります。

SELECT A.Username, A.Message
SUM(CASE WHEN `status` = 'Ok' THEN 1 ELSE 0 END) AS StatOK,
SUM(CASE WHEN `status` = 'Bad' THEN 1 ELSE 0 END) AS StatBAD
FROM db1.table1 as A
INNER JOIN db2.table2 as B 
ON A.Message = B.Message
WHERE A.Username = 'jamesbond'
GROUP BY A.Username, A.Message

私はこの結果を得ました：

+--------------+--------------------------+--------+---------+
| Username     | Message                  | StatOK | StatBAD |
+--------------+--------------------------+--------+---------+
| jamesbond    | I need some help         | 2      | 1       |
+--------------+--------------------------+--------+---------+

このような結果を取得する方法（DB2にステータスのないメッセージは引き続き表示されますが、SUMの結果はゼロまたはNULLになる可能性があります）：

+--------------+--------------------------+--------+---------+
| Username     | Message                  | StatOK | StatBAD |
+--------------+--------------------------+--------+---------+
| jamesbond    | I need some help         | 2      | 1       |
| jamesbond    | Mission accomplished     | NULL   | NULL    |
+--------------+--------------------------+--------+---------+
4

1 に答える 1

5

が必要ですLeft Outer Join。Leftテーブルから行を取得し、Rightテーブルと一致しない場合はNULLを取得します。

SELECT A.Username, A.Message
SUM(CASE WHEN `status` = 'Ok' THEN 1 ELSE 0 END) AS StatOK,
SUM(CASE WHEN `status` = 'Bad' THEN 1 ELSE 0 END) AS StatBAD
FROM db1.table1 as A
LEFT OUTER JOIN db2.table2 as B 
ON A.Message = B.Message
WHERE A.Username = 'jamesbond'
GROUP BY A.Username, A.Message
于 2012-10-03T04:41:14.930 に答える