Oracle - Count a select based on a subquery - sql

Question

I need to count the result from a sub query based on the main query
I would like to count how many Vehicle there are with the year 2021.
How would I generate the result of this query with a column counting each green car that has the year 2021. Example below
Table 1
ID
Vehicle
1
Car
2
motorcycle
3
bicycle
Table 2
ID
ID_TABLE1
COLOR
1
2
RED
2
1
GREEN
3
3
BLACK
4
1
GREEN
Table 3
ID
ID_TABLE1
YEAR
1
2
2021
2
1
2020
3
3
2021
3
1
2020
My try, its not working
select t1.Vehicle, t2.color from table1 t1 inner join table2 t2 on t1.id = t2.id_table1
left joint(select count* table 3 t3 where t3.year = 2020 ) tbyear on t1.id = t3.id_table1
The final table would look like this:
NAME
NAME
COUNT
CAR
green
2
motorcycle
red
0
bicycle
black
0

Answer 1

It should works like this if you want to see Year, Vehicle, color
select t3.Year, t1.Vehicle, t2.color, COUNT(*)
from table1 t1
inner join table2 t2 on t1.id = t2.id_table1
inner join table3 t3 on t1.id = t3.id_table1
GROUP BY t3.Year, t1.Vehicle, t2.color
If you don't need some filed - delete it in select and group by.
But it's not the best solution - when you haven't sales in 2021 for Green Car (for example)- you will not see it in a result query that's why i should ask: Do you need to see it? (for example 0 instead of skipping this row)
Am i correct about the task?

Answer 2

Looks like you want outer apply():
select
t1.Vehicle, t2.color, tbyear.*
from table1 t1
inner join table2 t2
on t1.id = t2.id_table1
outer apply(
select count(*) cnt
from table3 t3
where t1.id = t3.id_table1
and t3.year = 2020
) tbyear;
Full example with test data:
with -- test data:
Table1(ID,Vehicle) as (
select 1, 'Car' from dual union all
select 2, 'motorcycle' from dual union all
select 3, 'bicycle' from dual
)
,Table2(ID, ID_TABLE1, COLOR) as (
select 1, 2, 'RED' from dual union all
select 2, 1, 'GREEN' from dual union all
select 3, 3, 'BLACK' from dual union all
select 4, 1, 'GREEN' from dual
)
,Table3(ID,ID_TABLE1,YEAR) as (
select 1, 2, 2021 from dual union all
select 2, 1, 2020 from dual union all
select 3, 3, 2021 from dual union all
select 3, 1, 2020 from dual
)
-- end test data
select
t1.Vehicle, t2.color, tbyear.*
from table1 t1
inner join table2 t2
on t1.id = t2.id_table1
outer apply(
select count(*) cnt
from table3 t3
where t1.id = t3.id_table1
and t3.year = 2020
) tbyear
Results:
EHICLE COLOR CNT
---------- ----- ----------
motorcycle RED 0
Car GREEN 2
bicycle BLACK 0
Car GREEN 2