using STRING_AGG and the LAST_VALUE function in same request - sql-server

Question

How do I get the 777777 from the last record found in the order by id
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
to create table and data
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
The solution was
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;
thanks #Charlieface

Answer 1

You can put the window function in a derived table, and then use an aggregation function on it (either MIN or 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

You can use sub-query
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
Or you can parse the result of the aggregation and get the result from the string without the need of another query (no sub-query)
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
Check both solutions in your specific database and choose the one which provide you better performance (SSMS execution Plan analyze shows that second query is better but don't count on it and check IO and TIME in your server)