Mysql爲每個組選擇最後一行

Question

SELECT 
MAX('time'), c_id, message, state, time 
FROM message 
WHERE receive = 1 
GROUP BY c_id 

我有一個mysql查詢，我嘗試選擇每個組的最後一行，但它不工作。

c_id是組。它現在選擇每個組的第一行。

Answer 1

首先，您不應該使用單引號轉義列名，因爲它不是字符串文字。
其次，你可以做子查詢，每個子查詢分別獲得每個c_id的最新時間，並將它與原始表加入以獲取其他列。

SELECT a.* 
FROM message a 
     INNER JOIN 
     (
      SELECT c_id, MAX(time) time 
      FROM message 
      GROUP BY c_id 
     ) b ON a.c_id = b.c_id AND 
       a.time = b.time 

或

SELECT a.* 
FROM message a 
WHERE a.time = 
     (
      SELECT MAX(time) time 
      FROM message b 
      WHERE a.c_id = b.c_id 
     ) 

Answer 2

感謝名單吳宇森！

SELECT a.* FROM survey_question_option a INNER JOIN (
    SELECT subordinate_question, MAX(sort) sort 
    FROM  survey_question_option 
    WHERE  question_id=14 
    GROUP BY subordinate_question 
) b ON ((a.subordinate_question = b.subordinate_question) OR (a.subordinate_question IS NULL AND b.subordinate_question IS NULL)) AND 
a.sort = b.sort AND a.question_id=14;