SQL Last activity of given type - sql

Question

So I have a Visitor table, and a Visitor_activity table. Say:
Visitor
Visitor_ID Int
Visitor_name varchar(20)
Visitor_Activity
ID Int
Visitor_ID Int
Activity_Type char(3) -- values IN or OUT
Activity_Time datetime
Visitors might sign in and out multiple times in a day.
I'd like a nice query to tell me all visitors who are in: i.e. the last activity for today (on activity_time) was an "IN" not an "OUT". Any advice much appreciated.
It's T-SQL by the way, but I think it's more of an in-principle question.

Answer 1

One way to solve this is to use a correlated not exists predicate:
select Activity_Time, Visitor_ID
from Visitor_Activity t1
where Activity_Type = 'IN'
and not exists (
select 1
from Visitor_Activity
where Activity_Type = 'OUT'
and Visitor_ID = t1.Visitor_ID
and Activity_Time > t1.Activity_Time
and cast(Activity_Time as date) = cast(t1.Activity_Time as date)
)
This basically says get all visitor_id that have type = IN for which there doesn't exists any type = OUT record with a later time (on the same date).
Sample SQL Fiddle

Answer 2

SELECT
v.*
FROM
Visitors v
JOIN Visitor_Activity va ON va.Visitor_ID = v.Visitor_ID
WHERE
va.Activity_Type = 'IN'
AND NOT EXISTS ( SELECT
*
FROM
Visitor_Activity va_out
WHERE
va_out.Visitor_ID = va.Visitor_ID
AND va_out.Activity_Type = 'OUT'
AND va_out.Activity_Time > va.Activity_Time )

Answer 3

with visitorsInOut as (
select Visitor_id,
max(case when Activity_Type = 'in' then Activity_Time else null end) inTime,
max(case when Activity_Type = 'out' then Activity_Time else null end) outTime
from Visitor_Activity
where datediff(dd, Activity_Time, getdate()) = 0
group by Visitor_id)
select Visitor_id
from visitorsInOut
where inTime > outTime or outTime is null

Answer 4

This uses a CTE to find the activity record with the greatest Activity_Time where the Activity_Type = 'IN' and assigns it RowNum 1. Then you can INNER JOIN the CTE to the Visitor table, filtering by the CTE results where RowNum = 1.
; WITH VisAct AS(
SELECT act.Visitor_ID
, ROW_NUMBER() OVER(PARTITION BY Visitor_ID ORDER BY Activity_Time DESC) AS RowNum
FROM Visitor_Activity act
WHERE act.Activity_Type = 'IN'
AND act.Activity_Time >= CAST(GETDATE() AS DATE)
)
SELECT vis.Visitor_ID, vis.Visitor_name
FROM Visitor vis
INNER JOIN VisAct act
ON act.Visitor_ID = vis.Visitor_ID
WHERE act.Row_Num = 1

Answer 5

You can pull the most recent action for each visitor, and then only return those where the last action for today was to check in.
SELECT v.Visitor_ID, v.Visitor_Name, va.Activity_Type, va.Activity_Time
FROM Visitor AS v
INNER JOIN (SELECT Visitor_ID, Activity_Type, Activity_Time, RANK() OVER (PARTITION BY Visitor_ID ORDER BY Activity_Time DESC) AS LastAction
FROM Visitor_Activity
-- checks for today, can be omitted if you still want
-- to see someone checked in from yesterday
WHERE DATEDIFF(d, 0, Activity_Time) = DATEDIFF(d, 0, getdate())
) AS va ON va.Visitor_ID = v.Visitor_ID
WHERE LastAction = 1
AND Activity_Type = 'IN'

Answer 6

With CROSS APPLY:
DECLARE #d DATE = '20150320'
DECLARE #v TABLE
(
visitor_id INT ,
visitor_name NVARCHAR(MAX)
)
DECLARE #a TABLE
(
visitor_id INT ,
type CHAR(3) ,
time DATETIME
)
INSERT INTO #v
VALUES ( 1, 'A' ),
( 2, 'B' ),
( 3, 'C' )
INSERT INTO #a
VALUES ( 1, 'in', '2015-03-20 19:32:27.513' ),
( 1, 'out', '2015-03-20 19:32:27.514' ),
( 1, 'in', '2015-03-20 19:32:27.515' ),
( 2, 'in', '2015-03-20 19:32:27.516' ),
( 2, 'out', '2015-03-20 19:32:27.517' ),
( 3, 'in', '2015-03-20 19:32:27.518' ),
( 3, 'out', '2015-03-20 19:32:27.519' ),
( 3, 'in', '2015-03-20 19:32:27.523' )
SELECT *
FROM #v v
CROSS APPLY ( SELECT *
FROM ( SELECT TOP 1
type
FROM #a a
WHERE a.visitor_id = v.visitor_id
AND a.time >= #d
AND a.time < DATEADD(dd, 1, #d)
ORDER BY time DESC
) i
WHERE type = 'in'
) c
Output:
visitor_id visitor_name type
1 A in
3 C in
The principle:
First you are selecting all visitors.
Then you are applying to visitor last activity
SELECT TOP 1
type
FROM #a a
WHERE a.visitor_id = v.visitor_id
AND a.time >= #d
AND a.time < DATEADD(dd, 1, #d)
ORDER BY time DESC
Then you are selecting from previous step in order to get empty set which will filter out visitors whose last activity was not 'in'. If last activity was 'in' you get one row in result and thus applying works. If last activity is 'out' then outer query will result in empty set, and by design CROSS APPLY will eliminate such visitor.