2

我有 2 个表（它只是此查询所需的表列的一部分）： 

Items: Id int, OwnerId int
ItemsRelations: RelationId int, ItemId Int (FK Items(Id))

对于每个 OwnerId，我需要计算比率函数的结果：链接到 ItemsRelationstable 的用户元素计数/所有用户元素的计数。

我写了这个查询，但它很慢而且不是最优的。有没有更简单快捷的方法来做到这一点？

SELECT OwnerId , (100 * SUM(HasRelation))/COUNT(Id) AS Ratio
FROM (
  SELECT 
    oi.OwnerId,
    oi.Id,
    (CASE WHEN SUM(ir.Id) > 0 THEN 1 ELSE 0 END) HasRelation
  FROM Items AS oi
  LEFT JOIN ItemsRelations AS ir ON ir.ItemId  = oi.Id
  GROUP BY oi.Id, oi.OwnerId) tempTab 
GROUP BY OwnerId
4

2 回答 2

2 
SELECT oi.OwnerId, Ratio = 1.0 * Count(ir.ItemId) / Count(*)
FROM Items AS oi
LEFT JOIN ItemsRelations AS ir ON ir.ItemId  = oi.Id
GROUP BY oi.OwnerId

笔记：

  • 添加了1.0，将表达式转换为float结果
  • Count(ir.ItemId) 跳过 NULLS，所以它只计算那些有关系的

如果ItemstoItemsRelations是一对多，那么你可能需要区分它

SELECT oi.OwnerId, Ratio = 1.0 * Count(DISTINCT ir.ItemId) / Count(DISTINCT oi.Id)
FROM Items AS oi
LEFT JOIN ItemsRelations AS ir ON ir.ItemId  = oi.Id
GROUP BY oi.OwnerId
于 2012-02-17T11:05:20.737 回答
0

我认为这应该可以解决问题：

select i.OwnerId,
       case when count(i.Id) > 0 then count(r.Id)/count(i.Id) else 0 end as Ratio
from Items i
left join ItemsRelations r on r.ItemId = i.Id
group by i.Id, i.OwnerId
于 2012-02-17T11:02:09.387 回答