database - 带有 INNER JOIN 的 Postgres COUNT 列值数

Question

我正在 Postgres 9.3 中创建报告。这是我的SQL Fiddle .
基本上我有两个表，responses 和 questions，结构是:

responses
->id
->question_id
->response

questions
->id
->question
->costperlead

response 列只能有 3 个值，Yes/No/Possbily， 我的报告应该有以下栏目:

  question_id
, # of Yes Responses
, # of No Responses
, # of Possbily Responses
, Revenue

然后:

# of Yes Responses - count of all Yes values in the response column
# of No Responses - count of all No values in the response column
# of Possbily Responses - count of all 'Possbily' values in the response column

收入是 costperlead *(是的响应数 + 可能的响应数)。

我不知道如何构建查询，我是新手，而且我来自 MySQL，所以有些事情对于 postgres 是不同的。在我的 SQL Fiddle 示例中，大多数响应是 Yes 和 Null，最终没问题，可能会有和 No。

到目前为止我只有:

SELECT a.question_id
FROM responses a
INNER JOIN questions b ON a.question_id = b.id
WHERE a.created_at = '2015-07-17'
GROUP BY a.question_id;

Answer 1

你应该尝试:

SELECT a.question_id, 
       SUM(CASE WHEN a.response = 'Yes' THEN 1 ELSE 0 END) AS NumsOfYes, 
       SUM(CASE WHEN a.response = 'No' THEN 1 ELSE 0 END) AS NumsOfNo,
       SUM(CASE WHEN a.response = 'Possibly' THEN 1 ELSE 0 END) AS NumOfPossibly,
       costperlead  * SUM(CASE WHEN a.response = 'Yes' THEN 1 ELSE 0 END) + SUM(CASE WHEN a.response = 'Possibly' THEN 1 ELSE 0 END) AS revenue
FROM responses a 
     INNER JOIN questions b ON a.question_id = b.id 
GROUP BY a.question_id, b.costperlead