mysql：奇怪的错误1111无效使用group by

Question

Following is a query i am trying to run.

select location_data.trip_code,sum(max(device_time)-min(device_time)) from location_data,trip_management 
where location_data.source_id=3 and location_data.trip_code=trip_management.trip_code
group by location_data.trip_code

there are various trips identified by trip_code in both trip_managemnet and location_data tables.these trips are taken by a single uniquely identified user (source_id=)3. what i am trying to do here is to sum all the time differences for each trip and then convert it into hh:mm:ss using the sec_to_time function to display the total time it took user 3 to take all of his trips.

the problem with above query is that it generates error 1111 as soon as i apply sum() over the difference of max and min device_time of each trip. i cant afford a subquery because this in itself is a subquery in a larger query.

I hope i explained the problem well.

Answer 1

The issue here is that you are attempting to apply an aggregate SUM() over the aggregates MAX(),MIN() , but in fact the two levels operate on different groups. The inner one groups over location_data.trip_code , and the outer one groups over the result of that. You'll need to wrap it in a subquery:

SELECT
  trip_code,
  /* Outer query sums the inner aggregates */
  SUM(max_time - min_time) AS time_sum
FROM (
  SELECT 
    location_data.trip_code,
    /* Inner aggregates return the max & min times only */
    max(device_time) AS max_time,
    min(device_time) AS min_time
  FROM
     location_data,
     INNER JOIN trip_management ON location_data.trip_code = trip_management.trip_code
  WHERE
     location_data.source_id=3
  GROUP BY location_data.trip_code
) first_group
GROUP BY trip_code

I've also replaced you implicit join with an explicit INNER JOIN , which is the preferred syntax nowadays.