How do I insert left joins in a nested query? - sql

Question

First of all I would like to thank the friends who helped this complex and difficult query.
I have three tables
Table 1
StaffId FirstName LastName staffType
---------------------------------------
1 Adam Sorme Student
2 Lara Sandra Teacher
3 Jack Jones Student
Table 2
GateId GateName
---------------------------------------
1 frontDoor
2 superDoor
Table 3
Id transitionDate GateId StaffId
---------------------------------------
1 2018-01-1 08:00:00 1 1
2 2018-01-1 10:00:00 2 1
3 2018-01-1 20:00:00 2 1
4 2018-01-2 07:00:00 1 2
5 2018-01-2 10:00:00 1 3
6 2018-01-9 12:00:00 2 2
I want the first and last movements of students for each day. Value must be set to null if no movement is available between the specified dates
transitionDate> '2018-01-1 00:00:00 000'
and transitionDate< '2018-01-03 00:00:00 000'
OUTPUT:
Id Date MinTransitionDate MaxTransitionDate FirstGateName LastGateName StaffId StaffType
1 2018-01-01 2018-01-1 08:00:00 2018-01-1 20:00:00 frontDoor superDoor 1 Student
2 2018-01-01 null null null null 3 student
3 2018-01-02 null null null null 1 student
4 2018-01-02 2018-01-2 10:00:00 null frontDoor null 3 student
The following query is partially working.
select s.staffId, d.dte,
min(t.transitionDate) as first_change,
max(t.transitionDate) as first_change,
max(case when seqnum_asc = 1 then gateId end) as first_gateid,
max(case when seqnum_desc = 1 then gateId end) as last_gateid
from (select s.* from Staff s where stafftype = 'Student') s cross join
(select distinct cast(transitionDate as date) as dte from Transitions) d left join
(select t.*,
row_number() over (partition by StaffId, cast(transitionDate as date) order by transitionDate) as seqnum_asc,
row_number() over (partition by StaffId, cast(transitionDate as date) order by transitionDate desc) as seqnum_desc
from Transitions t
) t
on cast(t.transitiondate as date) = d.dte and
t.staffId = s.staffId and
1 in (t.seqnum_asc, t.seqnum_desc)
group by s.staffId, d.dte;
Here is a SQL Fiddle.
How do I add firstGateName and LastGateName to this query result?

Answer 1

You can just join your existing query to the Gates table to get those names, i.e.
<existing query>
inner join Gates g1 on g1.gateId = (required gate id)
In your case you can join using the aggregate value you've
select
q.*,
g1.GateName as first_gate_name,
g2.GateName as last_gate_name
from
-- use existing query as a subquery, so we can easily use the first/last_gateid values
(
select s.staffId, d.dte,
min(t.transitionDate) as first_change,
max(t.transitionDate) as last_change,
max(case when seqnum_asc = 1 then gateId end) as first_gateid,
max(case when seqnum_desc = 1 then gateId end) as last_gateid
from (select s.* from Staff s where stafftype = 'Student') s cross join
(select distinct cast(transitionDate as date) as dte from Transitions) d left join
(select t.*,
row_number() over (partition by StaffId, cast(transitionDate as date) order by transitionDate) as seqnum_asc,
row_number() over (partition by StaffId, cast(transitionDate as date) order by transitionDate desc) as seqnum_desc
from Transitions t
) t
on cast(t.transitiondate as date) = d.dte and
t.staffId = s.staffId and
1 in (t.seqnum_asc, t.seqnum_desc)
group by s.staffId, d.dte
) q
-- join on the appropriate gate ids
inner join Gates g1 on g1.gateId = q.first_gateid
inner join Gates g2 on g2.gateId = q.last_gateid