Nested JOIN to create custom dynamic columns - mysql

Question

I have a table veicoli (vehicles) like this:
-------------------------------
| ID | Modello | Targa |
-------------------------------
| 1 | IVECO | XA123WE |
-------------------------------
| 2 | IVECO | CF556XD |
-------------------------------
| 3 | FIAT | AS332ZZ |
-------------------------------
| 4 | GOLF | GF567YU |
-------------------------------
For each vehicle I have none, one or multiple revisioni_veicolo (revisions) (the one with bigger DateExpiring is the one I need to check if revision is still valid or not based on today date)
-------------------------------------------------------------------
| ID | veicoli_ID | DateExpiring | Pass_Success |
-------------------------------------------------------------------
| 1 | 1 | 2019-07-01 | 1
------------------------------------------------------------------
| 2 | 1 | 2020-10-01 | 0
-------------------------------------------------------------------
| 3 | 2 | 2019-11-25 | 1
-------------------------------------------------------------------
| 4 | 2 | 2018-10-20 | 1
-------------------------------------------------------------------
| 5 | 4 | 2017-10-20 | 1
-------------------------------------------------------------------
Based on my example above (today is 2019-10-29):
Vehicle: ID = 1 has a revision still active (2020-10-01) but not passed (Pass_success = 0)
Vehicle: ID = 2 has a revision still active (2019-11-25) and passed (Pass_success = 1)
Vehicle: ID = 3 has no revision yet
Vehicle: ID = 4 has revision, but no active revision (last expired on 2017-10-20) but the last one passed the check (Pass_success = 1)
What I need is to have 3 new custom columns created dynamically on my query result:
-------------------------------------------------------------------------------------------
| ID | Modello | Targa | RevisionPresent | RevisionStillActive | LastRevisionPassed |
-------------------------------------------------------------------------------------------
| 1 | IVECO | XA123WE | true | true | false
-------------------------------------------------------------------------------------------
| 2 | IVECO | CF556XD | true | true | true
-------------------------------------------------------------------------------------------
| 3 | FIAT | AS332ZZ | false | false | false
-------------------------------------------------------------------------------------------
| 4 | GOLF | GF567YU | true | false | true
-------------------------------------------------------------------------------------------
I tried to start with my old post: MYSQL INNER JOIN to get 3 types of result
But I'm very confused using nested JOIN
I tried starting a fiddle but i'm stuck on syntax error: http://sqlfiddle.com/#!9/3c70bf/2

Answer 1

You need a LEFT JOIN of the tables and conditional aggregation:
select v.ID, v.Modello, v.Targa,
max(r.DataScadenzaRevisione is not null) RevisionPresent,
coalesce(max(r.DataScadenzaRevisione >= current_date()), 0) RevisionStillActive,
max(case when r.DataScadenzaRevisione = g.maxdate then r.EsitoPositivo else 0 end) LastRevisionPassed
from veicoli v
left join revisioni_veicolo r on r.veicoli_ID = v.id
left join (
select veicoli_id, max(DataScadenzaRevisione) maxdate
from revisioni_veicolo
group by veicoli_id
) g on g.veicoli_ID = v.id
group by v.ID, v.Modello, v.Targa
See the demo.
Results:
| ID | Modello | Targa | RevisionPresent | RevisionStillActive | LastRevisionPassed |
| --- | ------- | ------- | --------------- | ------------------- | ------------------ |
| 1 | IVECO | XA123WE | 1 | 1 | 0 |
| 2 | IVECO | CF556XD | 1 | 1 | 1 |
| 3 | FIAT | AS332ZZ | 0 | 0 | 0 |
| 4 | GOLF | GF567YU | 1 | 0 | 1 |

Answer 2

...
LEFT JOIN (SELECT a.veicoli_ID, a.EsitoPositivo AS StatoUltimaRevisione,
a.DataScadenzaRevisione FROM revisioni_veicolo) a
...
There's two things wrong with this.
The alias a is defined for this subquery, so you can't reference it inside the subquery. But you don't need to qualify the columns in this subquery anyway - you didn't do this in other subqueries, so I'm not sure why you did it in this case.
You don't have any join condition for this join. MySQL is a little bit inconsistent about when join conditions are required. But in this case, you need one.
After I tested the query with these two corrections, it works.

Answer 3

Basically you just need to look at the last revision of each vehicule to produce that resultset.
You can do the filtering with a correlated subquery:
select
v.ID,
v.Modello,
v.Targa,
(DataScadenzaRevisione >= now()) RevisionPresent,
(DataScadenzaRevisione >= now() and EsitoPositivo = 1) RevisionStillActive,
(EsitoPositivo = 1) LastRevisionPassed
from
veicoli v
left join revisioni_veicolo r
on r.veicoli_ID = v.ID
and r.DataScadenzaRevisione = (
select max(DataScadenzaRevisione)
from revisioni_veicolo r1
where r1.veicoli_ID = v.ID
)
You can check the results with your sample data in this db fiddle.
Or you can use a window function (this requires MySQL 8.0):
select
v.ID,
v.Modello,
v.Targa,
(DataScadenzaRevisione >= now()) RevisionPresent,
(DataScadenzaRevisione >= now() and EsitoPositivo = 1) RevisionStillActive,
(EsitoPositivo = 1) LastRevisionPassed
from (
select
v.*,
r.*,
row_number() over(partition by ID order by r.DataScadenzaRevisione desc) rn
from veicoli v
left join revisioni_veicolo r on r.veicoli_ID = v.ID
) where coaelesce(rn, 1) = 1