Question

如何改进此查询？

select ID, Name
       ,(select top 1 Item FROM Items where BeneficiaryID = a.ID 
          order by PickupDateTime desc) as Item
       ,(select top 1 FontColor FROM Items where BeneficiaryID = a.ID 
          order by PickupDateTime desc) as FontColor
       ,(select top 1 BackColor FROM Items where BeneficiaryID = a.ID 
          order by PickupDateTime desc) as BackColor
FROM Beneficiary a
where Name like N'%Sam%'

当我尝试同一子查询中的3个字段时，我得到：

当EXISTS没有引入子查询时，只能在选择列表中指定一个表达式。

我需要获取受益人数据，其中包含存储在项目表中的最新项目。

我尝试使用左连接但没有获得所需的结果。

Answer 1

struct QuestionAnswerer {

    func responseTo() {

        //This makes all the caracters lower cased.
        let lowerQuestion = question.lowercased()

        if lowerQuestion.range(of: "Photos") != nil {
            myFunction()
        } else {
            myOtherFunction()
        }
    }
}

Answer 2

尝试使用cte clause＆amp; ROW_NUMBER（）

With itemsData as (
select BeneficiaryID, FontColor,BackColor, PickupDateTime
, row_number() over (partition by BeneficiaryID         order by PickupDateTime desc) rn
From items)
Select a.ID,a.Name,b.item,b.FontColor,b.Backcolor     
FROM Beneficiary a left join itemsData b on b.BeneficiaryID = a.ID and b.rn=1
where a.Name like N'%Sam%'

不带cte子句的查询

Select a.ID,a.Name,b.item,b.FontColor,b.Backcolor     
FROM Beneficiary a 
left join (select BeneficiaryID, FontColor,BackColor, PickupDateTime
, row_number() over (partition by BeneficiaryID    order by PickupDateTime desc) rn
From items) b on b.BeneficiaryID = a.ID and b.rn=1
where a.Name like N'%Sam%'

在select子句中，从子查询中获取多个字段

2 个答案: