Find min and max data column in Table - sql

Question

I have a table that specifies exactly what date and time each employee was in a particular office.
EmployeeTable looks like this:
id
EmployeeID
DateP
TimeP
1
11111
1397/01/02
01:30
2
11111
1398/05/09
05:30
3
11111
1398/06/07
05:10
4
22222
1398/08/09
06:12
5
22222
1399/02/01
07:15
6
11111
1399/07/02
08:51
7
11111
1399/08/06
12:20
8
33333
1399/09/04
20:01
9
33333
1399/12/08
22:05
10
33333
1400/01/01
23:11
11
33333
1400/02/05
14:10
12
22222
1400/04/05
16:25
I want exactly select Min and Max date and time for each Employee when present in a office:
id
EmployeeID
MinDateP
TimeMinDateP
MaxDateP
TimeMaxDateP
1
11111
1397/01/02
01:30
1398/06/07
05:10
2
22222
1398/08/09
06:12
1399/02/01
07:15
3
11111
1399/07/02
08:51
1399/08/06
12:20
4
33333
1399/09/04
20:01
1400/02/05
14:10
5
22222
1400/04/05
16:25
1400/04/05
16:25
My SQL code is:
with tab1 as
(
select *
from EmployeeTable
), tab2 as
(
select
t1.*,
case when lag(t1.EmployeeID) over(order by t1.id) is null then 1
when lag(t1.EmployeeID) over(order by t1.id) = t1.EmployeeID then 0
else 1
end lg
from tab1 t1
)
, tab3 as (
select t1.*,
sum(t1.lg) over(order by t1.id) grp
from tab2 t1
)
select t1.EmployeeID,
min(t1.DateP) as min,
TimeP,
max(t1.DateP)as max,
TimeP
from tab3 t1
group by t1.EmployeeID, t1.grp
But above codes has error.
Can every body help me?

Answer 1

This is a gaps and islands problem. One approach to solve this uses the difference in row numbers method:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY DateP, TimeP) rn1,
ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY DateP, TimeP) rn2
FROM EmployeeTable
),
cte2 AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY EmployeeID, rn1 - rn2
ORDER BY DateP, TimeP) rn_first,
ROW_NUMBER() OVER (PARTITION BY EmployeeID, rn1 - rn2
ORDER BY DateP DESC, TimeP DESC) rn_last
FROM cte
)
SELECT
EmployeeID,
MAX(CASE WHEN rn_first = 1 THEN DateP END) AS MinDateP,
MAX(CASE WHEN rn_first = 1 THEN TimeP END) AS TimeMinDateP,
MAX(CASE WHEN rn_last = 1 THEN DateP END) AS MaxDateP,
MAX(CASE WHEN rn_last = 1 THEN TimeP END ) AS TimeMaxDateP
FROM cte2
GROUP BY
EmployeeID,
rn1 - rn2
ORDER BY
MIN(DateP),
MIN(TimeP);
Note that the logic in the second CTE would be totally unnecessary if you were using a single datetime column to represent the date and time. It is usually not beneficial to separate date and time as you are currently doing.