每個結果合併Group BY和多個計數

Question

我是Oracle的新手，希望結果包含基於值的多個計數。例如：

SELECT p.name, count(f.id) as eaten_apples, count(f.id) as eaten_oranges 
FROM food f, people p 
WHERE f.pid=p.pid 
AND f.id = 'apple' OR f.id = 'orange' 
GROUP BY p.name; 

顯然具有計數（f.id）有兩次將各自產生相同的結果，但願望是具有每吃的食物的類型的一個計數。蘋果和橘子。預期結果可能如下所示：

[0] => 
    name : john 
    eaten_apples: 3 
    eaten_oranges: 1 
[1] => 
    name : sam 
    eaten_apples: 0 
    eaten_oranges: 9 
... 

換句話說，每個結果有多個計數。在這種情況下，一個人吃的食物數量。

我的查詢現在返回兩個每個名稱的結果，我可能在SQL之外組合，但我想從SQL結果每個名稱得到一個結果。

Answer 1

在Oracle中這樣分組並不習慣，但如果需要的話，它仍然是可能的。相反，更好的做法和我的建議是由name和id產生兩行，每個水果一行。

SELECT p.name, f.id, count(1) as eaten_fruit 
from food f, people p 
WHERE f.pid=p.pid 
AND (
     f.id = 'apple' OR 
     f.id = 'orange' 
    ) 
GROUP BY p.name, f.id; 

我相信，讓數據的應用程序句柄閱讀上面是更有效的，但正如我指出的那樣，有重新格式化選項。有a number of ways to transpose these row based results into columns和其他解決方案嘗試其中之一。我偏好的方法是使用專門爲此目的而引入的PIVOT operator。爲了得到結果，你想要的格式，你可以移調行轉換成列如：

select name, id from 
        (
         select p.name, f.id 
         from food f, people p 
         where f.pid = p.pid 
         and f.id in ('apple','orange') 
        ) 
pivot (
      count(id) 
      for id in (
         'apple' as eaten_apples, 
         'orange' as eaten_oranges 
        ) 
    ); 

它會工作，但不常見。

Answer 2

這裏是一個選擇，這將給在一個記錄每人吃蘋果和桔子的數量：

WITH cte AS 
(
    SELECT p.name, f.id 
    FROM people p LEFT JOIN food f 
     ON f.pid = p.pid 
) 

SELECT t1.name, COALESCE(t1.aCount, 0) AS eaten_apples, 
    COALESCE(t2.oCount, 0) AS eaten_oranges 
FROM people AS p 
LEFT JOIN 
(
    SELECT name, COUNT(name) AS aCount 
    FROM cte 
    WHERE id = 'apple' 
    GROUP BY name 
) AS t1 
    ON p.name = t1.name 
LEFT JOIN 
(
    SELECT name, COUNT(name) AS oCount 
    FROM cte 
    WHERE id = 'orange' 
    GROUP BY name 
) AS t2 
    ON p.name = t2.name