SQL GROUP BY - 检查具有不同值的列是否具有特定值

Question

I am new to working with SQL and I am not sure how to approach the following problem:

Imagine I got this table

User_ID | Operating System | LastSeen (containing some timestamps)
1       |  IOS             | hh:mm:ss   
1       |  AOS             | hh:mm:ss
1       |  Unknown         | hh:mm:ss
2       |  IOS             | hh:mm:ss
2       |  Unkown          | hh:mm:ss
3       |  AOS             | hh:mm:ss

UserID in combination with the OperatingSystem could be a primary key and is unique in each row

I want to get a user table (and therefore I wanna use group by User_ID) giving me the latest LastSeen Value (using Max(LastSeen)) as well as a boolean for usesAndroid and usesIOS.

so the result should look like

User ID | Using_IOS | USING_AOS | LastSeen containing Max(LastSeen)
1       | True      | True      | hh:mm:ss
2       | True      | False     | hh:mm:ss
3       | False     | True      | hh:mm:ss

Regarding the Using_IOS/Using_AOS columns, I am not sure how to get them in a group by, can I use sth like a contains or in function in a GroupBy for a column that contains multiple different values in a group?

Thanks in advance!

Answer 1

You can group on the user ID and use sum :

select user_id, sum(OperatingSystem = "IOS") > 0, sum(OperatingSystem = "AOS") > 0, max(LastSeen)
from test group by user_id