在同一请求中使用string_agg和last_value函数

Question

我如何从ID订单中找到的最后一个记录中获得777777，以

SELECT 
    STRING_AGG(name,'-') WITHIN GROUP (ORDER BY id) as names,
    STRING_AGG([numerToCall],'-') as calledNumbers,
    --LAST_VALUE([numerToCall])) OVER (ORDER BY id) as lastCalled
    '777777' as lastCalled
FROM 
    SimpleTest1

创建表格和数据。

 CREATE TABLE [dbo].[simpleTest1](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [name] [varchar](50) NOT NULL,
    [numerToCall] [varchar](50) NOT NULL,
 CONSTRAINT [PK_simpleTest1] PRIMARY KEY CLUSTERED 
    (
        [id] ASC
    )
) ON [PRIMARY]
SET IDENTITY_INSERT [dbo].[simpleTest1] ON 
INSERT [dbo].[simpleTest1] ([id], [name], [numerToCall]) VALUES (1, N'benny', N'555555')
INSERT [dbo].[simpleTest1] ([id], [name], [numerToCall]) VALUES (2, N'helle', N'999999')
INSERT [dbo].[simpleTest1] ([id], [name], [numerToCall]) VALUES (3, N'hans', N'777777')
SET IDENTITY_INSERT [dbo].[simpleTest1] OFF

解决方案是

SELECT 
    STRING_AGG(t.name,'-') WITHIN GROUP (ORDER BY id) as names,
    STRING_AGG(t.numerToCall, '-') as calledNumbers,
    MIN(t.xxxx) as lastCalled
FROM (
    SELECT *,
      LAST_VALUE(t.numerToCall) OVER (ORDER BY id ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) as xxxx
    from
    SimpleTest1 t
) t;

@Charlieface

Answer 1

您可以将窗口函数放入派生表中，然后对其使用聚合函数（MIN 或 MAX）

SELECT 
    STRING_AGG(t.name,'-') WITHIN GROUP (ORDER BY id) as names,
    STRING_AGG(t.numerToCall, '-') WITHIN GROUP (ORDER BY id) as calledNumbers,
    MIN(t.numerToCall]) as lastCalled
FROM (
    SELECT *,
      LAST_VALUE(t.numerToCall) OVER (ORDER BY id ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) as lastCalled
    SimpleTest1 t
) t;

Answer 2

您可以使用子查询

SELECT 
    STRING_AGG(t.name,'-') WITHIN GROUP (ORDER BY id) as names,
    STRING_AGG(t.[numerToCall],'-') WITHIN GROUP (ORDER BY id) as calledNumbers,
    --LAST_VALUE([numerToCall])) OVER (ORDER BY id) as lastCalled
    (SELECT TOP 1 InTbl.numerToCall FROM SimpleTest1 InTbl ORDER BY id desc) as lastCalled
FROM 
    SimpleTest1 t
GO

，也可以解析聚合的结果并从字符串中获取结果，而无需其他查询（无子查询）

SELECT 
    STRING_AGG(t.name,'-') WITHIN GROUP (ORDER BY id) as names,
    STRING_AGG(t.[numerToCall],'-') WITHIN GROUP (ORDER BY id) as calledNumbers,
    --LAST_VALUE([numerToCall])) OVER (ORDER BY id) as lastCalled
    RIGHT(STRING_AGG(t.[numerToCall],'-') WITHIN GROUP (ORDER BY id), CHARINDEX('-',REVERSE(STRING_AGG(t.[numerToCall],'-') WITHIN GROUP (ORDER BY id)))-1) as lastCalled
FROM 
    SimpleTest1 t
GO

检查您的特定数据库中的两个解决方案，然后选择为您提供更好性能的一个解决方案（SSMS执行计划分析表明，第二个查询更好，但不要依靠它，并在您的服务器中检查IO和时间）