MYSQL INNER JOIN 获得 3 种类型的结果

Question

I have a table VEHICLES like this:

-------------------------------------------------------
| ID  |   Brand   |   License_plate      |  Model      |
-------------------------------------------------------
| 1   |   IVECO   |   XA123WE            |  GRANDX    |
| 2   |   IVECO   |   CF556XD            |  TOURS     |
| 3   |   FIAT    |   AS332ZZ            |  Punto     |
-------------------------------------------------------

For each vehicle I have one or multiple INSURANCE (the one with bigger date is the one I need to check if insurance is still active or not based on today date)

-------------------------------------
| ID  |   vehicle_ID   |   Expire   |
-------------------------------------
| 1   |   1            | 2018-10-19 |
| 2   |   1            | 2019-10-20 |
| 3   |   2            | 2019-11-25 |
| 4   |   2            | 2018-10-20 |
-------------------------------------

In my example above, assuming today is 2019-10-28 , insurance for vehicle with ID 1 is expired, insurance for vehicle with ID 2 is still active (2019-11-25), vehicles ID 3 has no insurance yet.

I'm not sure how to build a unique query in PHP to get my result to search:

1. All vehicles ID with insurance expired (checking only the highest by date for each vehicle, if is < NOW() )

2. All vehicles ID with no insurance present

    SELECT V.ID FROM vehicles V JOIN insurance I ON V.ID = I.vehicle_ID WHERE....

3. All vehicles ID with insurance still active (checking only the highest by date for each vehicle, if is >= NOW() )

Answer 1

You coudl try using left join for the two condition

select  v.ID, v.Brand, v.Mode
    , ifnull(t1.max_expire_date, 'expired') expired
    ,  ifnull(t2.vehicle_ID , 'not present') not_present
    , case when t1.max_expire_date is not null then 'present' END AS present
from vehicles 
LEFT JOIN  (
  select  vehicle_ID, max(Expire) max_expire_date
  from  insurance 
  group by  vehicle_ID
) t1 on t1.vehicle_ID = v.id 
    AND t.max_expire_date >= date(NOW())
LEFT JOIN  (
  select  vehicle_ID
  from  insurance 
) t2 ON t2.vehicle_ID = v.id 

and if you want filter using a where condition you can't use the column alias but you should repeat the code

select  v.ID, v.Brand, v.Mode
    , ifnull(t1.max_expire_date, 'expired') expired
    ,  ifnull(t2.vehicle_ID , 'not present') not_present
    , case when t1.max_expire_date is not null then 'present' END AS present
from vehicles 
LEFT JOIN  (
  select  vehicle_ID, max(Expire) max_expire_date
  from  insurance 
  group by  vehicle_ID
) t1 on t1.vehicle_ID = v.id 
    AND t.max_expire_date >= date(NOW())
LEFT JOIN  (
  select  vehicle_ID
  from  insurance 
) t2 ON t2.vehicle_ID = v.id 
WHERE ifnull(t1.max_expire_date, 'expired')  = 'expired'

Answer 2

Using LEFT OUTER JOINs, you 3 queries could be done as:-

SELECT vehicles.ID 
FROM vehicles 
INNER JOIN insurance i1 
ON vehicles.ID = i1.vehicle_ID 
LEFT OUTER JOIN insurance i2 
ON i1.vehicle_ID = i2.vehicle_ID 
AND i2.expire > i1.expire
WHERE i2.id IS NULL
AND i1.expire < NOW()

Here it does a left outer join for any later insurance expiry dates, and checks for i2.id being NULL to ensure no later expiry date is found, and then checks the found expiry date to check it has expired.

SELECT vehicles.ID 
FROM vehicles 
LEFT OUTER JOIN insurance i1 
ON vehicles.ID = i1.vehicle_ID 
WHERE i1.id IS NULL

This just checks there is no matching insurance record

SELECT vehicles.ID 
FROM vehicles 
INNER JOIN insurance i1 
ON vehicles.ID = i1.vehicle_ID 
LEFT OUTER JOIN insurance i2 
ON i1.vehicle_ID = i2.vehicle_ID 
AND i2.expire > i1.expire
WHERE i2.id IS NULL
AND i1.expire >= NOW()

Very similar to the first query, it does a left outer join for any later insurance expiry dates, and checks for i2.id being NULL to ensure no later expiry date is found, and then checks the found expiry date to check it has not expired.