Question

原始表User

ID   Created_Date   SubmittedAt   ApprovedAt

原始表Campaign

User_ID   Clicked_At

现在我想生成一个包含

等列的报告

Month  Year  #Applicants  #Submitted  #Approved

我使用postgresql编写了查询：

SELECT To_char(C.clicked_at, 'MON')    AS MON, 
       Extract(year FROM C.clicked_at) AS YYYY, 
       CASE 
         WHEN created_date IS NOT NULL THEN Count(user_id) 
       END AS APPLICANTS, 
       CASE 
         WHEN submittedat IS NOT NULL THEN Count(user_id) 
       END AS SUBMITTED, 
       CASE 
         WHEN approvedat IS NOT NULL THEN Count(user_id) 
       END AS APPROVED 
FROM   campaign C, 
       users U 
WHERE  C.user_id = U.id 
GROUP  BY 1,2

我收到一条错误消息“u.created_date必须出现在GROUP BY子句中，或者在聚合函数中使用。但是，我只希望我的结果按year分组{ {1}}。

Answer 1

首先，使用正确的，明确的JOIN语法。其次，如果要计算非空值的数量，则可以简化代码：

SELECT TO_CHAR(C.CLICKED_AT, 'MON') AS MON,
       EXTRACT(YEAR FROM C.CLICKED_AT) AS YYYY,
       COUNT(CREATED_DATE) AS APPLICANTS,
       COUNT(SUBMITTEDATE) AS SUBMITTED,
       COUNT(APPROVEDAT) AS APPROVED
FROM CAMPAIGN C JOIN
     USERS U
     ON C.USER_ID = U.ID
GROUP BY 1, 2;

通过这种简化，您根本不再拥有任何（显式）条件逻辑，因此group by子句没问题。

我建议您将月份和年份结合起来并对结果进行排序：

SELECT TO_CHAR(C.CLICKED_AT, 'YYYY-MM') AS yyyymm,
       COUNT(CREATED_DATE) AS APPLICANTS,
       COUNT(SUBMITTEDATE) AS SUBMITTED,
       COUNT(APPROVEDAT) AS APPROVED
FROM CAMPAIGN C JOIN
     USERS U
     ON C.USER_ID = U.ID
GROUP BY 1
ORDER BY 1;

Answer 2

您需要将CASE语句放在聚合函数中：

SELECT TO_CHAR(C.CLICKED_AT,'MON') AS MON,
EXTRACT(YEAR FROM C.CLICKED_AT) AS YYYY,
COUNT(CASE WHEN CREATED_DATE IS NOT NULL THEN USER_ID END) AS APPLICANTS,
COUNT(CASE WHEN SUBMITTEDAT IS NOT NULL THEN USER_ID END) AS SUBMITTED,
COUNT(CASE WHEN APPROVEDAT IS NOT NULL THEN USER_ID END) AS APPROVED
FROM
CAMPAIGN C
JOIN USERS U ON C.USER_ID = U.ID
GROUP BY 1,2

注意：

如果您使用的是Postgres 9.4+，那么您可以使用FILTER子句。
使用显式JOIN子句代替WHERE子句来连接表
您可能会更好地扩展您的TO_CHAR()以接受年月

示例：

SELECT TO_CHAR(C.CLICKED_AT,'YYYY-MM') AS date_year_month,
COUNT(CASE WHEN CREATED_DATE IS NOT NULL THEN USER_ID END) AS APPLICANTS,
COUNT(CASE WHEN SUBMITTEDAT IS NOT NULL THEN USER_ID END) AS SUBMITTED,
COUNT(CASE WHEN APPROVEDAT IS NOT NULL THEN USER_ID END) AS APPROVED
FROM
CAMPAIGN C
JOIN USERS U ON C.USER_ID = U.ID
GROUP BY 1

如何使用Postgresql在一个报告中生成每月群组？

2 个答案: