SQL JOIN values to ARRAY to create another ARRAY field - sql

Question

maybe my searching is poor, but I couldn't find this question or answer anywhere.
Suppose I have a table CLASSROOM like:
[ { teacher_id: T1,
students: [S11, S12, S13]},
{ teacher_id: T2,
students: [S21, S22, S23]}]
The "students" field is an array of student_id's. There is also a table STUDENTS like:
[ { id: S11, name: "Aaron"}, { id: S12, name: "Bob"}, { id: S13, name: "Charlie"},
{ id: S21, name: "Amy"}, { id: S22, name: "Becky"}, { id: S23, name: "Cat"} ]
I want to create the output table which has rows like:
[ { teacher_id: T1,
students: [S11, S12, S13 ],
names: [ "Aaron", "Bob", "Charlie" ] },
{ teacher_id: T2,
students: [S21, S22, S23 ],
names: [ "Amy", "Becky", "Cat" ] } ]
(Yes, this example is silly, but I don't want to bore you with my case.)
I suppose I could FLATTEN the CLASSROOM table, then do a straight join, but my real table is large & complicated enough that I want to avoid it if I can. Is there a better way?
Note: assume students can be in multiple classes. Teachers (teacher_id) are unique.

Answer 1

The idea is to flatten the array and reaggregate. I'm not 100% sure of the syntax in Snowflake, but I think this will work:
select c.*,
(select array_agg(ss.name) within group (order by s.index) as student_names
from table(flatten(input => c.students, mode => 'array')) s join
students ss
on ss.id = s.value
) as names
from classroom c;

Answer 2

Based on https://stackoverflow.com/users/1144035/gordon-linoff, I got the following to work in Snowflake:
create table CLASSROOM (teacher_id VARCHAR, students ARRAY);
insert into CLASSROOM select $1, parse_json($2)
from values ('T1','["S11","S12","S13"]'),('T2','["S21","S22","S23"]');
create table STUDENTS (id VARCHAR, name VARCHAR);
insert into STUDENTS values ('S11','Aaron'),('S12','Bob'),('S13','Charlie'),('S21','Amy'),('S22','Becky'),('S23','Cat');
select teacher_id,
array_agg(s.value::String) as student_ids,
array_agg(ss.name) as student_names
from CLASSROOM, table(flatten(input => CLASSROOM.students, mode => 'array')) s
join STUDENTS ss on ss.id = s.value
group by teacher_id, s.SEQ
order by teacher_id;