每个结果合并Group BY和多个计数

Question

我是Oracle的新手，希望结果包含基于值的多个计数。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; 

显然具有计数（f.id）有两次将各自产生相同的结果，但愿望是具有每吃的食物的类型的一个计数。苹果和橘子。预期结果可能如下所示：

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

换句话说，每个结果有多个计数。在这种情况下，一个人吃的食物数量。

我的查询现在返回两个每个名称的结果，我可能在SQL之外组合，但我想从SQL结果每个名称得到一个结果。

Answer 1

在Oracle中这样分组并不习惯，但如果需要的话，它仍然是可能的。相反，更好的做法和我的建议是由name和id产生两行，每个水果一行。

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，让数据的应用程序句柄阅读上面是更有效的，但正如我指出的那样，有重新格式化选项。有a number of ways to transpose these row based results into columns和其他解决方案尝试其中之一。我偏好的方法是使用专门为此目的而引入的PIVOT operator。为了得到结果，你想要的格式，你可以移调行转换成列如：

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 
        ) 
    ); 

它会工作，但不常见。

Answer 2

这里是一个选择，这将给在一个记录每人吃苹果和桔子的数量：

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