Как написать функцию T-SQL STRING_AGG

Установите в вашей базе данных следующую внешнюю функцию

    /*
GROUP_CONCAT string aggregate for SQL Server - https://groupconcat.codeplex.com
Copyright (C) 2011  Orlando Colamatteo

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or 
any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

See http://www.gnu.org/licenses/ for a copy of the GNU General Public 
License.
*/

/*
Installation script for GROUP_CONCAT functions. Tested in SSMS 2008R2.
*/
SET NOCOUNT ON ;
GO

-- !! MODIFY TO SUIT YOUR TEST ENVIRONMENT !!
USE GroupConcatTest
GO

-------------------------------------------------------------------------------------------------------------------------------
 =-- Turn advanced options on
EXEC sys.sp_configure @configname = 'show advanced options', @configvalue = 1 ;
GO
RECONFIGURE WITH OVERRIDE ;
GO
 =-- Enable CLR
EXEC sys.sp_configure @configname = 'clr enabled', @configvalue = 1 ;
GO
RECONFIGURE WITH OVERRIDE ;
GO
-------------------------------------------------------------------------------------------------------------------------------
SET ANSI_NULLS, ANSI_PADDING, ANSI_WARNINGS, ARITHABORT, QUOTED_IDENTIFIER ON;
SET CONCAT_NULL_YIELDS_NULL, NUMERIC_ROUNDABORT OFF;
GO
IF EXISTS (SELECT * FROM tempdb..sysobjects WHERE id=OBJECT_ID('tempdb..#tmpErrors')) DROP TABLE #tmpErrors
GO
CREATE TABLE #tmpErrors (Error int)
GO
SET XACT_ABORT ON
GO
SET TRANSACTION ISOLATION LEVEL READ COMMITTED
GO
BEGIN TRANSACTION
GO
-------------------------------------------------------------------------------------------------------------------
PRINT N'Creating [GroupConcat]...';
GO
CREATE ASSEMBLY [GroupConcat]
    AUTHORIZATION [dbo]

    WITH PERMISSION_SET = SAFE;
GO
IF @@ERROR <> 0
   AND @@TRANCOUNT > 0
    BEGIN
        ROLLBACK;
    END
IF @@TRANCOUNT = 0
    BEGIN
        INSERT  INTO #tmpErrors (Error)
        VALUES                 (1);
        BEGIN TRANSACTION;
    END
GO
EXEC sys.sp_addextendedproperty 
    @name = N'URL',
    @value = N'http://groupconcat.codeplex.com',
    @level0type = N'ASSEMBLY',
    @level0name = N'GroupConcat'
GO
-------------------------------------------------------------------------------------------------------------------
PRINT N'Creating [dbo].[GROUP_CONCAT_D]...';
GO
CREATE AGGREGATE [dbo].[GROUP_CONCAT_D](@VALUE NVARCHAR (4000), @DELIMITER NVARCHAR (4))
    RETURNS NVARCHAR (MAX)
    EXTERNAL NAME [GroupConcat].[GroupConcat.GROUP_CONCAT_D];
GO
IF @@ERROR <> 0
   AND @@TRANCOUNT > 0
    BEGIN
        ROLLBACK;
    END
IF @@TRANCOUNT = 0
    BEGIN
        INSERT  INTO #tmpErrors (Error)
        VALUES                 (1);
        BEGIN TRANSACTION;
    END
GO
-------------------------------------------------------------------------------------------------------------------
PRINT N'Creating [dbo].[GROUP_CONCAT_S]...';
GO
CREATE AGGREGATE [dbo].[GROUP_CONCAT_S](@VALUE NVARCHAR (4000), @SORT_ORDER TINYINT)
    RETURNS NVARCHAR (MAX)
    EXTERNAL NAME [GroupConcat].[GroupConcat.GROUP_CONCAT_S];
GO
IF @@ERROR <> 0
   AND @@TRANCOUNT > 0
    BEGIN
        ROLLBACK;
    END
IF @@TRANCOUNT = 0
    BEGIN
        INSERT  INTO #tmpErrors (Error)
        VALUES                 (1);
        BEGIN TRANSACTION;
    END
GO
-------------------------------------------------------------------------------------------------------------------
PRINT N'Creating [dbo].[GROUP_CONCAT_DS]...';
GO
CREATE AGGREGATE [dbo].[GROUP_CONCAT_DS](@VALUE NVARCHAR (4000), @DELIMITER NVARCHAR (4), @SORT_ORDER TINYINT)
    RETURNS NVARCHAR (MAX)
    EXTERNAL NAME [GroupConcat].[GroupConcat.GROUP_CONCAT_DS];
GO
IF @@ERROR <> 0
   AND @@TRANCOUNT > 0
    BEGIN
        ROLLBACK;
    END
IF @@TRANCOUNT = 0
    BEGIN
        INSERT  INTO #tmpErrors (Error)
        VALUES                 (1);
        BEGIN TRANSACTION;
    END
GO
-------------------------------------------------------------------------------------------------------------------
PRINT N'Creating [dbo].[GROUP_CONCAT]...';
GO
CREATE AGGREGATE [dbo].[GROUP_CONCAT](@VALUE NVARCHAR (4000))
    RETURNS NVARCHAR (MAX)
    EXTERNAL NAME [GroupConcat].[GroupConcat.GROUP_CONCAT];
GO
IF @@ERROR <> 0
   AND @@TRANCOUNT > 0
    BEGIN
        ROLLBACK;
    END
IF @@TRANCOUNT = 0
    BEGIN
        INSERT  INTO #tmpErrors (Error)
        VALUES                 (1);
        BEGIN TRANSACTION;
    END
GO
-------------------------------------------------------------------------------------------------------------------
IF EXISTS (SELECT * FROM #tmpErrors) ROLLBACK TRANSACTION
GO
IF @@TRANCOUNT>0 BEGIN
PRINT N'The transacted portion of the database update succeeded.'
COMMIT TRANSACTION
END
ELSE PRINT N'The transacted portion of the database update failed.'
GO
DROP TABLE #tmpErrors
-------------------------------------------------------------------------------------------------------------------
GO

source https://archive.codeplex.com/?p=groupconcat

Затем вы можете использовать их в форме

**select BlogId, dbo.GROUP_CONCAT(Title) from Posts 
group by BlogId** 

ruselt

BlogId  (No column name)
1   Title 1,Title 2,Title 3,Title 11,Title 12,Title 13,Title 14,Title 
2   Title 29,Title 21,Title 10,Title 17,Title 15
3   Title 18,Title 5,Title 8,Title 28
4   Title 7,Title 19

Необходимо запустить CLR на сервере. Таким образом, когда база данных восстанавливается до новый сервер, CLR должен быть запущен

-- Turn advanced options on
EXEC sys.sp_configure @configname = 'show advanced options', @configvalue = 1 ;
GO
RECONFIGURE WITH OVERRIDE ;
GO
-- Enable CLR
EXEC sys.sp_configure @configname = 'clr enabled', @configvalue = 1 ;
GO
RECONFIGURE WITH OVERRIDE ;
GO