将> =更改为<=会导致查询超出执行时间限制

Question

I have a query that checks inventory for vehicles that have not been seen in a week but that are not listed in the sold_vehicles table.

If I run this query:

  SELECT all_vehicles.Vin
  FROM all_vehicles
  LEFT JOIN sold_vehicles
    ON all_vehicles.Vin = sold_vehicles.Vin
  WHERE
    sold_vehicles.id IS NULL        AND
    all_vehicles.last_seen >= 1502672069
  ORDER BY all_vehicles.id ASC
  LIMIT 1000

Everything works fine.

However, if I reverse the >= to <= it exceeds the 120 second execution time limit. Why would reversing this behave this way? Any reason other than a lot of results to return, and wouldn't the limit fix that?

To be clear, this is nearly the exact same query, but with <= and a LIMIT 10 yet fails to execute:

  SELECT all_vehicles.Vin
  FROM all_vehicles
  LEFT JOIN sold_vehicles
    ON all_vehicles.Vin = sold_vehicles.Vin
  WHERE
    sold_vehicles.id IS NULL        AND
    all_vehicles.last_seen <= 1502672069
  ORDER BY all_vehicles.id ASC
  LIMIT 10

Any ideas? Is it amount of results found alone? How do I fix it other than LIMIT ?

Answer 1

Start by removing the order by . Does this return anything?

SELECT av.Vin
FROM all_vehicles av LEFT JOIN
     sold_vehicles sv
     ON av.Vin = sv.Vin
WHERE sv.id IS NULL AND
      av.last_seen <= 1502672069
--ORDER BY av.id ASC
LIMIT 10;

Then, I would create indexes on all_vehicles(last_seen, Vin, id) and sold_vehicles(Vin, id) .