缺省MySQL值爲查詢結果

Question

列的默認值是否可以作爲查詢的結果，從而只要查詢該值就會自動更新值？

我有一個成員DB和取消表，我想members.NumberOfCancellations值自動填充到低於僞查詢的結果：

從取消選擇所有具有取消.date今天不到31天，其中cancellations.memberid等於$ phpvariable

我知道這可以用php和選擇/更新腳本來完成，但我希望phpmyadmin可能有這個功能？

______________________________________________________________ 
|memberid | firstname | lastname | numberofcancellations| 
______________________________________________________________ 
|1   | john  | doe  | resultofquery(= 2) | 
|2   | Dave  | Smith  | resultofquery (=1) | 
______________________________________________________________ 

___________________________________ 
|id |memberid | date | time | group | 
___________________________________ 
|1  |1   |2016-04-19 | 08:00 | 1  | 
|2  |2   |2016-04-18 | 13:00 | 4  | 
|3  |1   |2016-04-15 | 18:00 | 3  | 
_______________________________________________ 

Answer 1

如果您members表還沒有列在取消計數，然後將其添加：

UPDATE members t1 LEFT JOIN 
(
    SELECT memberid, COUNT(*) AS numberofcancellations 
    FROM cancellations 
    WHERE date BETWEEN CURDATE() - INTERVAL 30 DAY AND CURDATE() 
    GROUP BY memberid 
) t2 
    ON t1.memberid = t2.memberid 
SET t1.numberofcancellations = COALESCE(t2.numberofcancellations, 0) 

：

ALTER TABLE members ADD numberofcancellations int AFTER lastname; 

現在你可以用解除計更新members您將需要運行此查詢一次以初始填充新列。如果您想更新一個成員，那麼你可以添加一個WHERE條件的UPDATE聲明：

UPDATE members t1 LEFT JOIN 
(
    SELECT memberid, COUNT(*) AS numberofcancellations 
    FROM cancellations 
    WHERE date BETWEEN CURDATE() - INTERVAL 30 DAY AND CURDATE() 
    GROUP BY memberid 
) t2 
    ON t1.memberid = t2.memberid 
SET t1.numberofcancellations = COALESCE(t2.numberofcancellations, 0) 
WHERE t1.memberid = 1 -- or whatever value you want