How to find the number of passengers using Oracle 21c - sql

Question

I need your help to solve this problem in PL/SQL.
I'm learning PL/SQL and unfortunately I'm not very good at it and I need your help to solve this using a cursor.
I also created a DbFiddle for Oracle 21c because that's what I use and I apologize for not knowing how to separate text from code or how to edit a question correctly.
I put my attempt in the DbFiddle
https://dbfiddle.uk/uTFrwjsM
I just want to convert the script that goes in Sql Server to Oracle.
It is for educational purpose only.
Maybe you can help me please.
Thanks!
I will also put the data here
create table bus(
bus_id number,
arrival_time number,
capacity number);
insert into bus values(1,2,1);
insert into bus values(2,4,10);
insert into bus values(3,7,2);
commit;
select *
from bus;
create table passenger(
passenger_id number,
arrival_time number);
insert into passenger values(11,1);
insert into passenger values(12,1);
insert into passenger values(13,5);
insert into passenger values(14,6);
insert into passenger values(15,7);
commit;
Result
bus_id capacity b_arrival spot passenger_id p_arrival
1 1 2 1 11 1
2 10 4 1 12 1
2 10 4 2 NULL NULL
2 10 4 3 NULL NULL
2 10 4 4 NULL NULL
2 10 4 5 NULL NULL
2 10 4 6 NULL NULL
2 10 4 7 NULL NULL
2 10 4 8 NULL NULL
2 10 4 9 NULL NULL
2 10 4 10 NULL NULL
3 2 7 1 13 5
3 2 7 2 14 6
Thank you so much

Answer 1

Boneist asked for a solution using a single SELECT statement. Here is one, using not one but two MATCH_RECOGNIZE clauses! The basic idea is, SQL doesn't let us juggle two input streams, so I put the input into one stream and then figure out which rows to scrunch together.
select * from (
select BUS_ID, CAPACITY, SPOT, PASSENGER_ID,
coalesce(b.arrival_time, p.arrival_time) arrival_time
from bus b
cross apply(
select level spot from dual connect by level <= capacity
)
full join passenger p on 1=0
)
match_recognize (
order by arrival_time, PASSENGER_ID, spot
measures classifier() cl, match_number() mn,
case classifier() when 'B' then count(b.*) else count(p.*) end rn
all rows per match
pattern(p+ b+)
define b as bus_id is not null,
p as passenger_id is not null
)
match_recognize(
order by mn, rn, cl
measures first(bus_id) bus_id, first(capacity) capacity,
first(arrival_time) b_arrival, first(spot) spot,
last(passenger_id) passenger_id, last(arrival_time) p_arrival
pattern(a+)
define a as (mn, rn, 'B') = (( first(mn), first(rn), first(cl) ))
)

Answer 2

Based on your SQL Server code of:
DECLARE #id INT
DECLARE #arrival int
DECLARE cur CURSOR FOR
SELECT p.passenger_id, P.arrival_time
FROM dbo.passenger p
ORDER BY p.arrival_time, p.passenger_id
OPEN cur
FETCH NEXT FROM cur INTO #id, #arrival;
WITH cte_bus (bus_id, capacity, b_arrival, spot)
AS (
SELECT bus_id, capacity, arrival_time AS b_arrival, 1 AS spot FROM bus
UNION ALL
SELECT bus_id, capacity, b_arrival, spot+1 FROM cte_bus
WHERE spot < capacity
)
SELECT *, NULL AS passenger_id, NULL AS p_arrival
INTO #tmp
FROM cte_bus ORDER BY bus_id, spot
WHILE ##FETCH_STATUS = 0 BEGIN
UPDATE TOP (1) #tmp SET passenger_id = #id, p_arrival = #arrival WHERE b_arrival>=#arrival AND passenger_id IS NULL
FETCH NEXT FROM cur INTO #id, #arrival
END
CLOSE cur
DEALLOCATE cur
SELECT * FROM #tmp t
order by 1
I think what you need is to create a global temporary table (GTT), which is a permanent table but holds data on a per-session basis (n.b. the default is to delete data when a commit is issued after you have populated the GTT):
create global temporary table tmp (bus_id number,
capacity number,
b_arrival number,
spot number,
passenger_id number,
p_arrival number);
and the following does what you want:
BEGIN
-- initial population of the GTT
insert into tmp (bus_id,
capacity,
b_arrival,
spot)
WITH cte_bus (bus_id, capacity, b_arrival, spot)
AS (SELECT bus_id, capacity, arrival_time AS b_arrival, 1 AS spot FROM bus
UNION ALL
SELECT bus_id, capacity, b_arrival, spot+1 FROM cte_bus
WHERE spot < capacity)
SELECT bus_id,
capacity,
b_arrival,
spot
FROM cte_bus
ORDER BY bus_id,
spot;
-- loop through the passengers and assign them to a bus
for rec in (SELECT p.passenger_id, P.arrival_time
FROM passenger p
ORDER BY p.arrival_time, p.passenger_id)
loop
-- update the tmp GTT
-- find the lowest row that hasn't already got a passenger assigned
-- and update that row to assign the current passenger to it.
merge into tmp tgt
using (select bus_id,
capacity,
b_arrival,
spot,
row_number() over (order by bus_id, spot) rn
from tmp
where b_arrival >= rec.arrival_time
and passenger_id is null) src
on (tgt.bus_id = src.bus_id
and tgt.spot = src.spot
and src.rn = 1)
when matched then
update set tgt.passenger_id = rec.passenger_id,
tgt.p_arrival = rec.arrival_time;
END LOOP;
END;
/
See this dbfiddle for results.
I still think it would be possible to output the results just using a single SELECT statement (probably via use of the MODEL clause), but I lack the wherewithal to do that.

Answer 3

Another PL/SQL solution that works more like an old COBOL program from the '70s / '80s: just "merging" (in a non-SQL sense) two result sets.
create or replace force type t_bus_passenger as object(
bus_id number,
b_arrival number,
capacity number,
spot number,
passenger_id number,
p_arrival number
)
/
create or replace type tt_bus_passenger as table of t_bus_passenger
/
create or replace function bus_passenger_schedule
return tt_bus_passenger pipelined is
cursor cur_bp is
select t_bus_passenger(
BUS_ID, ARRIVAL_TIME, CAPACITY, SPOT, null, null
) obj
from bus, lateral(
select level spot from dual
connect by level <= capacity
)
order by arrival_time, spot;
cursor cur_passenger is
select * from passenger
order by arrival_time, passenger_id;
rec_passenger cur_passenger%rowtype;
begin
open cur_passenger;
fetch cur_passenger into rec_passenger;
for rec_bp in cur_bp loop
if rec_bp.obj.b_arrival >= rec_passenger.arrival_time then
rec_bp.obj.passenger_id := rec_passenger.passenger_id;
rec_bp.obj.p_arrival := rec_passenger.arrival_time;
fetch cur_passenger into rec_passenger;
end if;
pipe row(rec_bp.obj);
end loop;
close cur_passenger;
return;
end;
/
select * from bus_passenger_schedule();