選擇這導致對GROUP返回由

Question

行

考慮下面的查詢：

SELECT domain, done FROM tasks WHERE 1 GROUP BY domain 

很明顯，我可以得到它與MAX（完成）返回「完成」的最大值，但我如何得到它返回整行？

在我的情況，我有以下行的表：

domain = somedomain.com, done = 12:27:39, somecolumn = pink 
domain = somedomain.com, done = 13:27:39, somecolumn = blue 
domain = somedomain.com, done = 14:27:39, somecolumn = orange 
domain = anotherdomain.com, done = 07:27:39, somecolumn = orange 
domain = anotherdomain.com, done = 09:27:39, somecolumn = pie 

使用上面的查詢時，它返回以下2行：

domain = somedomain.com, done = 13:27:39, somecolumn = blue 
domain = anotherdomain.com, done = 09:27:39, somecolumn = pie 

我需要返回這2行：

domain = somedomain.com, done = 14:27:39, somecolumn = blue 
domain = anotherdomain.com, done = 09:27:39, somecolumn = pie 

感謝幫助:)。

Answer 1

最簡單的一個：

SELECT done,somecolumn FROM tasks ORDER BY done DESC LIMIT 1; 

更爲精細的查詢，左連接或可能需要子查詢，但是這一次是相當直截了當。

---

對於它的赫克，如果你確實需要的其他數據：

（1）NOT EXISTS：

SELECT a.* 
FROM tasks a 
WHERE NOT EXISTS(
    SELECT * FROM tasks b 
    WHERE b.domain = a.domain AND b.done > a.done); 

（2）LEFT JOIN

SELECT a.* 
FROM tasks a 
LEFT JOIN tasks b 
ON b.domain = a.domain AND b.done > a.done 
WHERE b.id IS NULL; 

（ 3）ROWNUMBER（）如：

SELECT numbered.* 
FROM (
    SELECT 
     @row := IF(@old_domain = domain,@row + 1,1) as rownumber, 
     @old_domain := domain as domain, 
     done, 
     somecolumn 
    FROM tasks 
    JOIN (SELECT @old_domain:=0,@row:=0) void 
    ORDER BY domain ASC, done DESC 
) numbered 
WHERE numbered.rownumber = 1; 

哪一個會給你更好的表現很大程度上取決於數據集，所以我只是測試這些。

Answer 2

SELECT * FROM tasks WHERE done = (SELECT Max(done) FROM tasks) 

Answer 3

select 
    * 
from 
    tasks 
where 
    `done`=(select max(`done`) from tasks)