计算行并从多个表中获取最新的日期

Question

我有2个表，Customer和CustomerActivity，如下图所示：

我想输出一个表：

• 包含来自Customer表的所有列，其中CustomerType ='Existing Customer'，另外还有2列：
• totalActivity（count activityID） - 显示每个客户的总活动数。
• latestActivity（max checkinTime） - 显示最近的活动日期时间

到目前为止，我有这两个查询，但我不知道如何组合/加入和过滤它们以获得我需要的东西。任何人都可以帮助1个查询（并且一些解释将是完美的）

SELECT customerId, firstName, birthDate, customerType 
FROM Customer 
WHERE Customer.customerType = 'Existing Customer'

SELECT t1.activityId, t1.checkinTime, t1.customerId
FROM CustomerActivity t1
inner join (
    SELECT customerId, max(checkinTime) as Lastest
    FROM CustomerActivity
    group by customerId
) t2 on t1.customerId = t2.customerId and t1.checkinTime = t2.Lastest

Answer 1

你真的很亲密。以下是您的查询应该是什么样的：

SELECT
    c.customerId,
    c.firstName,
    c.lastName,
    c.birthDate,
    c.customerType,
    ca.totalActivity,
    ca.latestActivity
FROM Customer c
INNER JOIN(
    SELECT 
        customerId, 
        latestActivity = MAX(checkinTime),
        totalActivity = COUNT(*)
    FROM CustomerActivity
    GROUP BY customerId
) ca
    ON ca.customerId = c.customerId
WHERE
    c.customerType = 'Existing Customer'

子查询（在INNER JOIN内）使用COUNT(*)检索活动总数，并使用每个客户的MAX(checkinTime)检索最新活动。之后，您可以将其加入Customer上的customerId表格。然后，您只需添加WHERE子句即可过滤'Existing Customer'。

Answer 2

我还没有针对实际模式对其进行测试，但是这样的事情应该有效（即使他们没有活动，这种方法也会向客户显示，如果您只想要客户，则只需将左连接更改为内连接活性）：

SELECT c.CustomerID
    , c.FirstName
    , c.BirthDate
    , c.CustomerType
    , COUNT(ca.ActivityID) AS TotalActivity
    , MAX(ca.CheckinTime) AS MostRecentActivity
FROM Customer c
LEFT JOIN CustomerActivity ca ON c.CustomerID = ca.CustomerID
WHERE c.CustomerType = 'Existing Customer'
GROUP BY c.CustomerID
    , c.FirstName
    , c.BirthDate
    , c.CustomerType

Answer 3

通过使用group by和窗口替换，您可以在不row_number()的情况下获得所需内容：

SELECT c.*, ca.numActivities, ca.activityId as LastActivity
FROM Customer c JOIN
     (select ca.*,
             count(*) over (partition by ca.CustomerId) as numActivities
             row_number() over (partition by ca.CustomerId order by checkinTime desc) as seqnum
      from CustomerActivity ca
     ) ca
     on c.customerId = ca.customerId and ca.seqnum = 1
WHERE c.customerType = 'Existing Customer';

此版本可让您从最近的活动行中获得您喜欢的任何列。

编辑：

在你原来的问题中，我认为你想要最新的活动。如果您只想要最新的日期时间，那么聚合就可以了：

SELECT c.*, ca.numActivities, ca.lastActivityDateTime
FROM Customer c JOIN
     (select ca.*,
             count(*)  as numActivities
             max(checkinTime) as lastActivityDateTime
      from CustomerActivity ca
     ) ca
     on c.customerId = ca.customerId
WHERE c.customerType = 'Existing Customer';

Answer 4

Select c.customerId, c.firstName, c.lastName, c.birthDate, c.customerType, gca.latestCheckIn, gca.count
from customer as c, 
    (select ca.customerId, max(ca.checkInTime) as latestCheckIn, count(*) as checkinCount 
    from customerActivity as ca
    group by ca.customerId) as gca
where gca.customerId = c.customerId AND c.customerType = 'Existing Customer'

如果您详细说明没有活动的客户，可以将查询更改为使用左连接