sql select，获取每辆车的最新条目

Question

My database (MySql) has 2 tables

Table 1 - contains a record for each car

cars= id(int), reg(int), type(int)

Table 2 - contains jobs for each car

jobs = id(int),date(date)

I need a SELECT command which will get me the most recent job for all id's

Thanks in advance.

Answer 1

You don't have a shared field, you cant do this. You need to store the associated car_id with each job, or have a jobs_to_cars table.

Then you'd use:

SELECT C.*, J.id, MAX(J.date)
FROM cars C 
INNER JOIN jobs J on J.car_id = C.id
GROUP BY C.id

If job's id IS the same as car's id then change j.car_id to j.id, but then you'd be lacking primary key on Jobs, which i suggest youd start making.

Answer 2

You could use something like this

SELECT c.*, MAX(j.date) date
FROM cars c 
   LEFT JOIN jobs j ON j.id = c.id
GROUP BY c.id
ORDER BY c.id

because you don't have other fields in [jobs]. If a car don't have any jobs, date will be NULL.

Answer 3

    SELECT *
      FROM cars c
INNER JOIN (SELECT MAX(id) AS j_id
              FROM jobs
          GROUP BY car_id) x ON x.j_id = c.id

1. You forgot the jobs.car_id field, that specifies which car job belongs to
2. More elegant way will be to create the field car.last_job_id and maintain it with trigger on jobs table.

Since your question is not clear, this query also can be an answer:

    SELECT j.*
      FROM jobs j
INNER JOIN (SELECT MAX(id) id
              FROM jobs
          GROUP BY car_id) x ON x.id = j.id

Answer 4

你可以试试

ORDER BY date DESC