Question

我正在Android中开发一个应用程序来显示我家乡的公交路线，我有问题有了查询，我的应用程序中有两个表，如下所示：

表格信息

ID | NAME     | DIRECTION
--------------------------
 1 | BUS 1    | departure
 2 | BUS 1    | return
 3 | BUS 2    | departure
 4 | BUS 2    | return
 5 | BUS 3    | departure
 6 | BUS 3    | return

表COORDINATES

ID | INFORMATION_ID |     LAT   |     LON       |
-------------------------------------------------
 1 |    1           | 19.171184 | -96.174029    |
 2 |    1           | 19.171021 | -96.173991    |
 3 |    1           | 19.171002 | -96.173979    |
 5 |    2           | 19.193244 | -96.138732    |
 6 |    2           | 19.193368 | -96.138957    |
 7 |    2           | 19.193332 | -96.138741    |

我试图在500米范围内显示附近的公交线路，我实际上可以通过此查询进行此操作

SELECT DISTINCT NAME,
((example.lat  - COORDINATES.LAT) * (example.lat - COORDINATES.LAT) + (example.lon - COORDINATES.LON) * (example.lon - COORDINATES.LON)) AS DISTANCE  
FROM COORDINATES
INNER JOIN INFORMATION
ON COORDINATES.INFORMATION_ID=INFORMATION.ID 
WHERE DISTANCE < 0.000023544  //supposedly 500 m, im not sure
ORDER BY DISTANCE

但问题是我在NAME字段中重复了值，因为我有几个来自该范围内的总线路径的latlon点，我只需要使用相应的名称返回最小距离，如下所示：

ID | NAME     | DISTANCE
---------------------
 1 | BUS 1    | 1.349834...
 3 | BUS 2    | 1.367033...

我希望找到解决此问题的任何指导，谢谢。

Answer 1

看看这是否有助于缩短距离。

SELECT NAME, MIN(DISTANCE) FROM
(
SELECT NAME, 
((19.171150  - COORDINATES.LAT) * (19.171184 - COORDINATES.LAT) + 
 (-96.173990 - COORDINATES.LON) * (-96.173990 - COORDINATES.LON)) AS DISTANCE  
FROM COORDINATES
INNER JOIN INFORMATION
ON COORDINATES.INFORMATION_ID=INFORMATION.ID 
WHERE DISTANCE < 0.000023544
) 
GROUP BY NAME

http://sqlfiddle.com/#!7/2e1ea/4

不同的返回重复项与多列

1 个答案: