Question

我有以下示例表

User | Event 
=============
Bob    EventX
Steve  EventA
Bob    EventC
Jane   EventB
Jane   EventA
Bob    EventC

我想构建一个真值表，告诉我特定用户是否触发了特定事件

User | EventA | EventB | Event C | Event X
===============================================
Bob     False    False    True      True
Steve   True     False    False     False
Jane    True      True    False     False

在SQL中有没有办法解决这个问题，而不必编写代码来构建这个表？

谢谢

Answer 1

尝试类似：

SELECT user, max(iif(event='EventA','True','False')) as 'EventA', .. 
FROM events
GROUP BY user;

Answer 2

您可以使用Pivot（下面的MSSQL示例）执行此操作。您必须在Pivot FOR（..）列表中指定每列

DECLARE @Events AS TABLE
    (
    EventId     VARCHAR(20)
    ,UserName   VARCHAR(100)
    )

INSERT INTO @Events (EventId, UserName)  VALUES('EventA','BOB')
INSERT INTO @Events (EventId, UserName)  VALUES('EventA','STEVE')
INSERT INTO @Events (EventId, UserName)  VALUES('EventB','STEVE')
INSERT INTO @Events (EventId, UserName)  VALUES('EventB','STEVE')
INSERT INTO @Events (EventId, UserName)  VALUES('EventB','STEVE')


SELECT
      PivotedList.UserName 
     ,CASE WHEN PivotedList.EventA IS NULL THEN 'FALSE' ELSE 'TRUE' END AS EventA
     ,CASE WHEN PivotedList.EventB IS NULL THEN 'FALSE' ELSE 'TRUE' END AS EventB

FROM
    @Events AS Events

    PIVOT 
    (
    MAX(EventId)
    FOR EventId IN ([EventA],[EventB])

    ) AS PivotedList

结果：

UserName    EventA  EventB
=================================
BOB         TRUE    FALSE
STEVE       TRUE    TRUE

在SQL中构建真值表

2 个答案: