慢SQL查询,不确定如何优化

Question

所以我必须处理一个没有索引的数据库(不是我的设计,它让我感到沮丧).我正在运行一个大约需要三秒钟才能返回的查询,我需要它更快.

以下是相关的表格和列:

gs_pass_data          au_entry            ground_station
  -gs_pass_data_id      -au_id              -ground_station_id
  -start_time           -gs_pass_data_id    -ground_station_name
  -end_time             -comments
  -ground_station_id

我的疑问是:

SELECT DISTINCT gs_pass_data_id,start_time,end_time,
  ground_station_name FROM gs_pass_data 
  JOIN ground_station
  ON gs_pass_data.ground_station_id =
  ground_station.ground_station_id 
  JOIN au_entry ON au_entry.gs_pass_data_id =
  gs_pass_data.gs_pass_data_id
WHERE (start_time BETWEEN @prevTime AND @nextTime) 
  AND comments = 'AU is identified.'
  ORDER BY start_time

我尝试过使用EXISTS代替DISTINCT而没有任何改进.我已经阅读了关于SQL优化的所有内容,但我似乎无法将此查询缩短到合理的时间(合理的<0.5秒).任何想法将不胜感激.

Answer 1

没有索引,你就被软管了.数据库引擎每次都必须进行全表扫描.摆弄查询只是重新安排泰坦尼克号上的躺椅.现在修复数据库,在数据堆积之前变得更糟.

Answer 2

查询也可以不用distinct 而是用group by 来编写。不过，它可能根本没有区别。标准建议与其他人的建议相同。添加索引，将 'order by' so +1 添加到 @Marc B

SELECT gs_pass_data_id,start_time,end_time,ground_station_name 
  FROM gs_pass_data 
  JOIN ground_station
    ON gs_pass_data.ground_station_id = ground_station.ground_station_id 
  JOIN au_entry 
    ON au_entry.gs_pass_data_id = gs_pass_data.gs_pass_data_id
 WHERE (start_time BETWEEN @prevTime AND @nextTime) 
   AND comments = 'AU is identified.'
 GROUP BY gs_pass_data_id,start_time,end_time,ground_station_name 
 ORDER BY start_time