MySQL的GROUP BY和計算行問題

Question

讓我們說MySQL的是這樣的

select x,y 
from xx 
group by y 

我想知道有多少行是選擇會得到，我試圖用計數，但它不會返回所有結果因爲我正在使用group。

該怎麼辦？

感謝

Answer 1

你可以用你的查詢，像這樣：

SELECT COUNT(*) FROM 
    (select x,y 
    from xx 
    group by y) sub; 

Answer 2

假設你有一個表與下面的內容：

------------------- 
| ID | NAME | GROUP | 
+-------------------+ 
| 1 | A | 1 | 
+-------------------+ 
| 2 | B | 2 | 
+-------------------+ 
| 3 | C | 2 | 
+-------------------+ 
| 4 | D | 3 | 
+-------------------+ 
| 5 | E | 1 | 
+-------------------+ 
| 6 | F | 3 | 
+-------------------+ 

以下自LEFT JOIN計數的數量GROUP中不同的值。

SELECT COUNT(*) 
FROM table AS t1 
LEFT JOIN table AS t2 ON t2.GROUP = t1.GROUP AND t2.ID > t1.ID 
WHERE t2.id IS NULL; 

此查詢所做的是找出每個組中具有最高ID的元素。

Answer 3

您可以檢查我的ANS https://stackoverflow.com/a/36449637/2439715

SELECT 
    sum(1) as counttotal 
FROM (
    Your query with group by operator 
) as T