BigQuery - 标量子查询产生了不止一个元素

Question

我有以下数据

LastSubmission          | PatientName | Phone   | SubmissionId | HealthCondition
2020-12-17 16:02:56 UTC |  a          |123456789| abc123       | Good
2020-12-18 14:24:33 UTC |  a          |123456789| abc123       | Bad
2020-12-18 14:24:51 UTC |  b          |523456789| def321       | okay
2020-12-18 14:25:09 UTC |  b          |523456789| def321       | bad
2020-12-21 17:11:40 UTC |  c          |623456789| hij987       | better
2020-12-21 17:05:30 UTC |  c          |623456789| hij981       | worse

我想编写一个只返回每个 SubmissionId 的最新数据的查询

目前，我有以下代码 -

SELECT *
FROM `myproject.dataset.qualtrics`
WHERE LastSubmission = 
( 
SELECT MAX(LastSubmission), 
FROM `myproject.dataset.qualtrics` 
GROUP BY SubmissionID, LastSubmission
) 
;

但是当我运行它时，我收到一条错误消息，提示“标量子查询产生了多个元素”请帮我解决这个问题。

Answer 1

你想要一个相关的子查询：

SELECT q.*
FROM `myproject.dataset.qualtrics` q
WHERE LastSubmission = (SELECT MAX(q2.LastSubmission) 
                        FROM `myproject.dataset.qualtrics` q2
                        WHERE q2.SubmissionID = q.SubmissionID
                       ) ;

编写查询的一种更“大查询”的方式是使用聚合：

select array_agg(q order by q.LastSubmission desc limit 1)[ordinal(1)].*
from `myproject.dataset.qualtrics` q
group by q.SubmissionID;