復雜的SQL查詢（COUNT，DISTINCT，大小寫，LEFT OUTER JOIN）

Question

我有兩張桌子

用戶：

+------------+-----------+
| user_id    | company   |
+------------+-----------+
| 1          | Apple     |
| 2          | Microsoft |
+------------+-----------+

會議：

+------------+---------+------------+-----------+------------+
| session_id | user_id | start_time | end_time  | user_agent |
+------------+---------+------------+-----------+------------+
| 1          | 1       | 12:00:00   | 12:20:00  | X          |
| 2          | 1       | 14:10:00   | 14:14:00  | Y          |
+------------+---------+------------+-----------+------------+

我想在一個查詢中查詢兩個表，並具有如下所示的輸出：

+------------+-----------+--------------------+
| user_id    | company   | unique_user_agents |
+------------+-----------+--------------------+
| 1          | Apple     | 2                  |
| 2          | Microsoft | 0                  |
+------------+-----------+--------------------+

帶有這樣的查詢：

x
SELECT users.user_id, users.company_name, COUNT(DISTINCT (case when sessions.start_time >= '11:00:00' AND sessions.end_time <= '15:30:00' then sessions.user_agent)) FROM users GROUP BY users.user_id LEFT OUTER JOIN sessions ON users.user_id = sessions.user_id

但是我在語法方面遇到錯誤，我知道這是錯誤的，但是我無法重新安排以取得成功。

有任何想法嗎？

Answer 1

總是以end並且在所有聯接之后必須保留group by的情況

SELECT users.user_id, users.company_name, COUNT(DISTINCT case when sessions.start_time >= '11:00:00' AND sessions.end_time <= '15:30:00' then sessions.user_agent end) 
FROM users 
LEFT OUTER JOIN sessions 
  ON users.user_id = sessions.user_id
GROUP BY users.user_id