联合查询问题
SELECT exam_sort.ID,exam_sort.Title,exam_station_sort.Must,exam_time.Locaton,exam_time.StartTime,exam_time.EndTime,exam_time.ExamDate,count(DISTINCT exam_sort.Title) FROM exam_sort
LEFT JOIN exam_station_sort ON
exam_station_sort.Sort = exam_sort.ID
LEFT JOIN exam_time ON exam_time.SID = exam_station_sort.StationNum
LEFT JOIN exam_student ON
exam_student.SID = exam_station_sort.StationNum
WHERE exam_station_sort.StationNum = ‘ “.$stationNum. ” ‘
AND exam_time.Sort = exam_station_sort.Sort
AND exam_station_sort.Must = 0
AND exam_sort.ID IN ( “.$soID[ “SortE “]. “)
AND exam_student.UserName = ‘ “.$userName. ” ‘
GROUP BY exam_sort.Title
ORDER BY exam_sort.ID
SELECT Sort,Title,Results FROM exam_results
WHERE SID = ‘ “.$stationNum. ” ‘
AND UserName = ‘ “.$userName. ” ‘
AND Sort IN ( “.$soID[ “SortE “]. “)
GROUP BY Title
ORDER BY Sort
以上两条 sql 语句中 exam_sort.Title与 Title 是一样的， exam_sort.ID 与 Sort 也是一样的，但是经常会出现 顺序不一样的查询结果，请问为什么？
GROUP BY exam_sort.Title
ORDER BY exam_sort.ID
用group by title 后 那个order by id 还有用吗?
