SQL：连接中的限制和随机化结果

Question

我正在构建一个可以在附近位置查找商品的购物系统。基本上，每个位置（供应商）在一个名为 Location 的表中都有一个条目，其中包含名称、纬度、经度和其他列......然后有一个项目表，带有一个外键，用于标识项目所属的位置到。

基本上，我想找到用户附近的所有项目：我可以使用以下查询来完成：

但是我想执行以下操作 - 从该位置随机选择物品 - 将每个位置的项目数量限制在少数（比如 5 个） - 随机化所有结果，使其不按位置分组

到目前为止，这是我完成的最困难的查询，我正在变得更好，但我一直坚持这个问题 - 如果非常感谢，请提供任何帮助！谢谢！！

到目前为止，这是我的选择语句：

SELECT Location.idLocation
 , Location.locationName
 , Location.tagline
 , Location.tags
 , Location.shortAddress
 , (3959 * acos(cos(radians('40.181')) * cos(radians(Location.latitude)) * cos(radians(Location.longitude) - radians('-74.0265')) + sin(radians('40.181')) * sin(radians(Location.latitude)))) AS distance
 , Item.idItem
 , Item.dateAdded
 , Item.fidLocation
 , Item.itemName
 , Item.description
 , Item.fullImageName
 , Item.thumbnailImageName
FROM
  Location
INNER JOIN Item
ON Location.idLocation = Item.fidLocation
HAVING distance < '1000'

Answer 1

好的。这是基于假设的未经测试的版本。

SELECT
  Location.idLocation,
  Location.locationName,
  Location.tagline,
  Location.tags,
  Location.shortAddress,
  (3959 * acos(cos(radians('40.181')) * cos(radians(Location.latitude)) * cos(radians(Location.longitude) - radians('-74.0265')) + sin(radians('40.181')) * sin(radians(Location.latitude)))) AS distance,
  Item.idItem,
  Item.dateAdded,
  Item.fidLocation,
  Item.itemName,
  Item.description,
  Item.fullImageName,
  Item.thumbnailImageName
FROM Location
  INNER JOIN (select *
          from Item
          order by RAND()
          limit 5) as Item
    ON Location.idLocation = Item.fidLocation
ORDER BY RAND()
HAVING distance < '1000'

Answer 2

SET @local = 0;
SET @group = 0;

SELECT Location.idLocation
 , Location.locationName
 , Location.tagline
 , Location.tags
 , Location.shortAddress
 , (3959 * acos(cos(radians('40.181')) * cos(radians(Location.latitude)) * cos(radians(Location.longitude) - radians('-74.0265')) + sin(radians('40.181')) * sin(radians(Location.latitude)))) AS distance
 , Item.idItem
 , Item.dateAdded
 , Item.fidLocation
 , Item.itemName
 , Item.description
 , Item.fullImageName
 , Item.thumbnailImageName
 , @level := IF(@group = idLocation, @level+1, 1) AS level
 , @group := idLocation as tempGroup 
FROM
  Location
INNER JOIN Item
ON Location.idLocation = Item.fidLocation
order by idLocation, RAND(),
HAVING distance < '1000' AND level <= 5