Find user online time - sql

Question

Having a question on how to write a self-join query.
The Online Session Table holds all user activities. Each Activity has a State ID, TimeStap to record the User login time.
It's like:
example:
State TimeStamp User
X 1300 A
Y 1700 A
X 0700 B
Z 1500 B
Y 1600 B
X 2100 C
A little Explanation: In the above table, User A logged in State X on 1300, then logged in State Y on 1700, so the User A spend 0400(assume it's 4 hours) in State X.
The Same logic applied to User B.
Then User C, since it never change sate, so we use current time - login time stamp of X.
The output should look like:
State Time User
X 0400(or 4) A
X 0800(or 8) B
Z 0100(or 1) B
X result of Now-2100 C
.......
Edit: Just make the problem clearer.Now let's assume it's in SQL Server DMBS,but it's ok to use other DBMS.
And input timestamps are store as default datetime format like YYYY-MM-DD HH:MM:SS.

Answer 1

You didn't mention which DBMS you're using, so I'm writing this how I'd do it in MS SQL Server (TSQL). You'll need access to the LAG function, which is not universal.
What LAG does is allow you to compare values from a previous row, based on some shared column value, in this case User. This code catches those comparisons in the prev_ fields. I'm using count() to differentiate users with more than one line from users with only one line. The single-line users are handled separately after the union all.
You'll notice that I'm not using your field names until the final output step. This is because State, Timestamp and User are all reserved words, i.e. words that do something in SQL code. I strongly recommend you use field names that are not reserved words.
This code does have a major limitation; it doesn't work for the now-minus-time portion if it's not the same day. So in your example, it would have to be between 21:01 and 23:59 the same day for it to work. If you wanted to do this robustly you'd use datetime format for your times, which would make this a lot easier and eliminate the limitation. But this answer is for your data, so:
SELECT
b.prev_state AS [State]
,b.Online_time - b.prev_time AS [Time]
,b.U_ID as [User]
FROM
(SELECT
t.Online_state
,t.U_ID
,t.Online_time
,LAG(t.online_time) OVER (PARTITION BY t.U_ID ORDER BY t.U_ID, t.online_time) AS prev_time
,LAG(t.online_state) OVER (PARTITION BY t.U_ID ORDER BY t.U_ID, t.online_time) AS prev_state
FROM online_t AS t
inner join
(SELECT
U_ID,
count(U_ID) AS tot
FROM online_t
GROUP BY U_ID) AS a
on t.U_ID = a.U_ID
WHERE tot > 1) AS b
WHERE prev_time is not null
union all
SELECT
t.Online_state AS [State]
,concat(datepart(hh,getdate()),'00') - t.Online_time AS [Time]
,t.U_ID AS [USER]
FROM online_t AS t
inner join
(SELECT
U_ID
,count(U_ID) as tot
FROM online_t
GROUP BY U_ID) as a
on t.U_ID = a.U_ID
WHERE tot = 1

Answer 2

I have a solution using Oracle analytical functions, which may not be available to you. I'm also using timestamps as oracle varchars.
I'm using LEAD() in a subquery to return the "next user" and the "next time".
Then using a CASE statement to handle the different scenarios.
SELECT M.THESTATE,
CASE
WHEN M.USERID = M2.NEXT_USER THEN M2.NEXT_TIME-M.THETIME
WHEN M.USERID <> M2.NEXT_USER THEN NULL
ELSE M.THETIME-0 END AS TOTALTIME
,M.USERID
FROM MYTEST M
JOIN
(
SELECT USERID, THESTATE, THETIME
,LEAD(THETIME) OVER (ORDER BY USERID, THETIME) AS NEXT_TIME
,LEAD(USERID) OVER (ORDER BY USERID, THETIME) AS NEXT_USER
FROM MYTEST
ORDER BY USERID
) M2 ON M2.USERID = M.USERID AND M2.THESTATE=M.THESTATE
WHERE
CASE
WHEN M.USERID = M2.NEXT_USER THEN M2.NEXT_TIME-M.THETIME
WHEN M.USERID <> M2.NEXT_USER THEN NULL
ELSE M.THETIME-0 END
IS NOT NULL;

Answer 3

Including your input in a WITH clause (I use the TIMESTAMP type for your "timestamp"; and some databases don't like if you use reserved words ("user", "timestamp") for column names), try this:
WITH
-- input, don't use in query
input(state,"timestamp","user") AS (
SELECT 'X',TIMESTAMP '2017-03-15 13:00:00','A'
UNION ALL SELECT 'Y',TIMESTAMP '2017-03-15 17:00:00','A'
UNION ALL SELECT 'X',TIMESTAMP '2017-03-15 07:00:00','B'
UNION ALL SELECT 'Z',TIMESTAMP '2017-03-15 15:00:00','B'
UNION ALL SELECT 'Y',TIMESTAMP '2017-03-15 16:00:00','B'
UNION ALL SELECT 'X',TIMESTAMP '2017-03-15 21:00:00','C'
)
,
-- start real query here, comma above would
-- be the WITH keyword
state_duration_user AS (
SELECT
state
, IFNULL(
LEAD("timestamp") OVER(ORDER BY "timestamp")
, CURRENT_TIMESTAMP
) - "timestamp"
AS "time"
, "user"
FROM input
)
SELECT
state
, CAST(SUM("time") AS TIME(0)) AS "time"
, "user"
FROM state_duration_user
GROUP BY
state
, "user"
;
state|time |user
Y |04:00:00|A
Y |01:00:00|B
Z |01:00:00|B
X |02:00:00|A
X |06:00:00|B
X |07:59:19|C