Mysql查詢提取日期+天數組

Question

簡單問題：爲什麼以下查詢不輸出perday？

SELECT FROM_UNIXTIME(`date`,"%Y-%m-%d") AS `perday`, COUNT(*) AS `count` 
FROM `data` 
WHERE `group` = 1 
GROUP BY `perday` 

計數得到正確輸出，但perday保持空。 的data表是這樣的：

| id | group |   date   | 
------------------------------------------------ 
| 1 |  1  | 2013-04-13 06:01:02 | 
| 2 |  1  | 2013-04-13 14:24:18 | 
| 3 |  2  | 2012-01-21 21:33:03 | 
       Ect. 

謝謝！

編輯：

預期輸出：

| perday | 
-------------- 
| 2013-04-13 | 
| 2012-01-21 | 

Answer 1

刪除WHERE條款，

SELECT FROM_UNIXTIME(date,'%Y-%m-%d') AS perday, 
     SUM(`group` = 1) AS `count` 
FROM data 
GROUP BY FROM_UNIXTIME(date,'%Y-%m-%d') 

如果日期的格式爲2013-04-13 06:01:02，那麼爲什麼要使用FROM_UNIXTIME？是不是DATE_FORMAT呢？

SELECT DATE_FORMAT(date, '%Y-%m-%d') AS perday, 
     SUM(`group` = 1) AS `count` 
FROM data 
GROUP BY DATE(date) 
ORDER BY date 

這將顯示錶中的所有可用日期。

• SQLFiddle Demo

但是如果你只想要選擇group，

SELECT DATE_FORMAT(date, '%Y-%m-%d') AS perday, 
     COUNT(*) AS `count` 
FROM data 
WHERE `group` = 1 
GROUP BY DATE(date) 
ORDER BY date 

Answer 2

你可以找這個

SELECT DATE_FORMAT(`date`,"%Y-%m-%d") AS `perday`, COUNT(*) AS `count` 
    FROM `data` 
    WHERE `group` = 1 
    GROUP BY `perday` 

DEMO HERE

Answer 3

MySQL DATE()將DATE部分從DATETIME表達式中提取出來。作爲Expected output，此查詢沒有問題。

SELECT 
    DATE(`date`) AS `perday`, 
    COUNT(*) AS `count` 
FROM `data` 
GROUP BY `perday`