Get the longest and shortest "chains" in MySQL? - mysql

Question

Consider this schema:
create table Operation(id integer, name varchar(100));
create table Pipeline(operation_in integer, operation_out integer);
Pipeline has foreign keys to Operations, so pipelines are chained, in a way. operation_out is nullable. How do I get the names of operations in both the longest and the shortest pipeline chains using MySQL?
Operations look like this:
INSERT INTO Operation VALUES (1, 'operation one');
While the pipelines look something like this:
INSERT INTO Pipeline VALUES (1, 2);
INSERT INTO Pipeline VALUES (2, 4);
INSERT INTO Pipeline VALUES (4, 7);
INSERT INTO Pipeline VALUES (7, NULL);
I.e. the chain here would be operations with ID 1, 2, 4, 7 and expected result along the lines of:
"operation one", "operation two", "operation four"...
After a few hours of research, I am not sure quite what the solution I am looking for.
Any MySQL version is applicable.

Answer 1

In MySQL 8.x you can use a Recursive CTE to find the chains you need.
For example:
with recursive
a as (
select
p.operation_in,
p.operation_out as current_out,
o.name as op_names,
concat('', p.operation_in) as chain,
1 as size
from pipeline p
join operation o on o.id = p.operation_in
where not exists (
select 1 from pipeline p2 where p2.operation_out = p.operation_in
)
union all
select
a.operation_in,
p.operation_out,
concat(op_names, ', ', o.name),
concat(chain, ',', p.operation_in),
size + 1
from a
join pipeline p on p.operation_in = a.current_out
join operation o on o.id = p.operation_in
),
chains as (
select * from a where current_out is null
)
select op_names, chain, size
from chains
where size = (select max(size) from chains) -- finds the longest one
or size = (select min(size) from chains); -- finds the shortest one
Result:
op_names chain size
--------------------------------- ------- ----
op-nine, op-six 9,6 2
op-one, op-two, op-four, op-seven 1,2,4,7 4
The data script I used is:
create table operation (id integer, name varchar(100));
create table pipeline (operation_in integer, operation_out integer);
insert into operation values (1, 'op-one');
insert into operation values (2, 'op-two');
insert into operation values (4, 'op-four');
insert into operation values (6, 'op-six');
insert into operation values (7, 'op-seven');
insert into operation values (9, 'op-nine');
insert into pipeline values (1, 2);
insert into pipeline values (2, 4);
insert into pipeline values (4, 7);
insert into pipeline values (7, null);
insert into pipeline values (9, 6);
insert into pipeline values (6, null);