SQL Server - How to concatenate rows by grouping data by one column (Grouped concatenation)

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Hello people,
Good afternoon!

In this post I will talk about a well-requested feature for Microsoft, and that it has not natively created natively in SQL Server, which is data concatenation using collations, already present in other DBMSs such as MySQL (GROUP_CONCAT), Oracle (XMLAGG) and PostgreeSQL ( STRING_AGG or ARRAY_TO_STRING (ARRAY_AGG ())).

A lot of people think this feature is the CONCAT () function, introduced in SQL Server 2012, but it only allows the concatenation of multiple columns of one row in one column and not the concatenation of multiple rows in one column.

Concatenating columns into grouped strings consists of transforming rows into a concatenated string so that you can group the values by some field, and the other column is concatenated, as shown below:

To create our test table, use the commands below:

IF (OBJECT_ID('dbo.Teste_Group_Concat') IS NOT NULL) DROP TABLE dbo.Teste_Group_Concat
CREATE TABLE dbo.Teste_Group_Concat(
    Categoria VARCHAR(100),
    Descricao VARCHAR(100)
)

INSERT INTO dbo.Teste_Group_Concat( Categoria, Descricao )
VALUES ('Brinquedo', 'Bola'),
('Brinquedo', 'Carrinho'),
('Brinquedo', 'Boneco'),
('Brinquedo', 'Jogo'),
('Cama e Mesa', 'Toalha'),
('Cama e Mesa', 'Edredom'),
('Informatica', 'Teclado'),
('Informatica', 'Mouse'),
('Informatica', 'HD'),
('Informatica', 'CPU'),
('Informatica', 'Memoria'),
('Informatica', 'Placa-Mae'),
(NULL, 'TV')

IF (OBJECT_ID('dbo.Teste_Group_Concat') IS NOT NULL) DROP TABLE dbo.Teste_Group_Concat

CREATE TABLE dbo.Teste_Group_Concat(

Categoria VARCHAR(100),

Descricao VARCHAR(100)

)

INSERT INTO dbo.Teste_Group_Concat( Categoria, Descricao )

VALUES ('Brinquedo', 'Bola'),

('Brinquedo', 'Carrinho'),

('Brinquedo', 'Boneco'),

('Brinquedo', 'Jogo'),

('Cama e Mesa', 'Toalha'),

('Cama e Mesa', 'Edredom'),

('Informatica', 'Teclado'),

('Informatica', 'Mouse'),

('Informatica', 'HD'),

('Informatica', 'CPU'),

('Informatica', 'Memoria'),

('Informatica', 'Placa-Mae'),

(NULL, 'TV')

COALESCE

How to concatenate columns in grouped strings using COALESCE

DECLARE @Nomes VARCHAR(MAX)

SELECT 
    @Nomes = COALESCE(@Nomes + ', ', '') + Descricao
FROM 
    dbo.Teste_XML

SELECT @Nomes

DECLARE @Nomes VARCHAR(MAX)

SELECT

@Nomes = COALESCE(@Nomes + ', ', '') + Descricao

FROM

dbo.Teste_XML

SELECT @Nomes

As we can see above, using the COALESCE function, we always need to store the results in a variable, and for this reason, we cannot get the results grouped by category as we need. If you just want to convert columns to a string, without grouping, this solution will suit you, but not what we need for this post.

STUFF + FOR XML PATH

How to concatenate columns in grouped strings using STUFF + FOR XML PATH

A practical and performative way to solve this problem is to use FOR XML PATH and STUFF to perform grouped concatenation, so the result is exactly what we expected:

SELECT  
    Categoria,
    STUFF((
        SELECT ', ' + B.Descricao 
        FROM dbo.Teste_Group_Concat B 
        WHERE ISNULL(B.Categoria, '') = ISNULL(A.Categoria, '')
        ORDER BY B.Descricao 
        FOR XML PATH('')), 1, 2, ''
    ) AS Descricao
FROM
    dbo.Teste_Group_Concat A
GROUP BY 
    Categoria
ORDER BY 
    Categoria

SELECT

Categoria,

STUFF((

SELECT ', ' + B.Descricao

FROM dbo.Teste_Group_Concat B

WHERE ISNULL(B.Categoria, '') = ISNULL(A.Categoria, '')

ORDER BY B.Descricao

FOR XML PATH('')), 1, 2, ''

) AS Descricao

FROM

dbo.Teste_Group_Concat A

GROUP BY

Categoria

ORDER BY

Categoria

UPDATED

How to concatenate columns in grouped strings using UPDATE

DECLARE 
    @Categoria VARCHAR(MAX),
    @Descricoes VARCHAR(MAX)
 
DECLARE @Tabela TABLE (
    Categoria VARCHAR(200),
    Descricao VARCHAR(200),
    Descricoes VARCHAR(200)
)
 
INSERT @Tabela ( 
    Categoria,
    Descricao
)
SELECT  
    Categoria,
    Descricao
FROM
    dbo.Teste_Group_Concat
ORDER BY 
    Categoria,
    Descricao
 

UPDATE 
    @Tabela
SET
    @Descricoes = Descricoes = COALESCE(CASE COALESCE(@Categoria, '')
                                WHEN Categoria THEN @Descricoes + ', ' + Descricao
                                ELSE Descricao
                            END, ''),
    @Categoria = ISNULL(Categoria, '')


SELECT  
    Categoria,
    Descricoes = MAX(Descricoes)
FROM
    @Tabela
GROUP BY 
    Categoria
ORDER BY 
    Categoria

DECLARE

@Categoria VARCHAR(MAX),

@Descricoes VARCHAR(MAX)

DECLARE @Tabela TABLE (

Categoria VARCHAR(200),

Descricao VARCHAR(200),

Descricoes VARCHAR(200)

)

INSERT @Tabela (

Categoria,

Descricao

)

SELECT

Categoria,

Descricao

FROM

dbo.Teste_Group_Concat

ORDER BY

Categoria,

Descricao

UPDATE

@Tabela

SET

@Descricoes = Descricoes = COALESCE(CASE COALESCE(@Categoria, '')

WHEN Categoria THEN @Descricoes + ', ' + Descricao

ELSE Descricao

END, ''),

@Categoria = ISNULL(Categoria, '')

SELECT

Categoria,

Descricoes = MAX(Descricoes)

FROM

@Tabela

GROUP BY

Categoria

ORDER BY

Categoria

Another solution that allowed us to generate the data as our needs demand.

LOOPING WITH CURSOR

How to concatenate columns in grouped strings using LOOPING with CURSOR

DECLARE @Tabela TABLE (
    Categoria VARCHAR(MAX),
    Descricoes VARCHAR(MAX)
)
 
INSERT @Tabela ( 
    Categoria,
    Descricoes
)
SELECT  
    Categoria,
    ''
FROM
    dbo.Teste_Group_Concat
GROUP BY 
    Categoria
 

DECLARE 
    @Categoria VARCHAR(MAX),
    @Descricao VARCHAR(MAX),
    @Descricoes VARCHAR(MAX)
 
DECLARE c CURSOR LOCAL FAST_FORWARD
FOR

    SELECT  
        Categoria,
        Descricao
    FROM
        dbo.Teste_Group_Concat
    ORDER BY 
        Categoria,
        Descricao
 

OPEN c
 
FETCH c INTO @Categoria, @Descricao
 
WHILE @@FETCH_STATUS = 0
BEGIN

    UPDATE  @Tabela
    SET     Descricoes += ', ' + @Descricao
    WHERE   ISNULL(Categoria, '') = ISNULL(@Categoria, '')
 
    FETCH c INTO @Categoria, @Descricao
END
 
CLOSE c
DEALLOCATE c

SELECT  
    Categoria,
    Descricoes = STUFF(Descricoes, 1, 1, '')
FROM
    @Tabela
ORDER BY 
    Categoria

DECLARE @Tabela TABLE (

Categoria VARCHAR(MAX),

Descricoes VARCHAR(MAX)

)

INSERT @Tabela (

Categoria,

Descricoes

)

SELECT

Categoria,

FROM

dbo.Teste_Group_Concat

GROUP BY

Categoria

DECLARE

@Categoria VARCHAR(MAX),

@Descricao VARCHAR(MAX),

@Descricoes VARCHAR(MAX)

DECLARE c CURSOR LOCAL FAST_FORWARD

FOR

SELECT

Categoria,

Descricao

FROM

dbo.Teste_Group_Concat

ORDER BY

Categoria,

Descricao

OPEN c

FETCH c INTO @Categoria, @Descricao

WHILE @@FETCH_STATUS = 0

BEGIN

UPDATE @Tabela

SET Descricoes += ', ' + @Descricao

WHERE ISNULL(Categoria, '') = ISNULL(@Categoria, '')

FETCH c INTO @Categoria, @Descricao

END

CLOSE c

DEALLOCATE c

SELECT

Categoria,

Descricoes = STUFF(Descricoes, 1, 1, '')

FROM

@Tabela

ORDER BY

Categoria

This solution also met what we need, but like all looping, it's not performative. I particularly abhor the creation of cursors (unless you are STILL on SQL Server 2000), as a last resort I prefer to use WHILE, but we have better solutions here in this post.

LOOPING WITH WHILE

How to concatenate columns in grouped strings using LOOPING with WHILE

DECLARE @Tabela_Original TABLE (
    Id INT IDENTITY(1, 1),
    Categoria VARCHAR(MAX),
    Descricao VARCHAR(MAX)
)
INSERT @Tabela_Original ( 
    Categoria,
    Descricao
)
SELECT  
    Categoria,
    Descricao
FROM
    dbo.Teste_Group_Concat
ORDER BY
    Categoria


DECLARE @Tabela TABLE (
    Id INT IDENTITY(1, 1),
    Categoria VARCHAR(MAX),
    Descricoes VARCHAR(MAX)
)

INSERT @Tabela ( 
    Categoria,
    Descricoes
)
SELECT  
    Categoria,
    ''
FROM
    dbo.Teste_Group_Concat
GROUP BY 
    Categoria
 
DECLARE 
    @Categoria VARCHAR(MAX),
    @Descricao VARCHAR(MAX),
    @Descricoes VARCHAR(MAX),
    @Contador INT = 1,
    @Numero_Linhas INT = (SELECT COUNT(*) FROM @Tabela_Original)
 
 WHILE(@Contador <= @Numero_Linhas)
 BEGIN

    SELECT  
        @Categoria = ISNULL(Categoria, ''),
        @Descricao = Descricao
    FROM
        @Tabela_Original
    WHERE
        Id = @Contador
    ORDER BY 
        Categoria,
        Descricao
    

    UPDATE  @Tabela
    SET     Descricoes += ', ' + @Descricao
    WHERE   ISNULL(Categoria, '') = ISNULL(@Categoria, '')


    SET @Contador = @Contador + 1

END


SELECT  
    Categoria,
    Descricoes = STUFF(Descricoes, 1, 1, '')
FROM
    @Tabela
ORDER BY 
    Categoria

DECLARE @Tabela_Original TABLE (

Id INT IDENTITY(1, 1),

Categoria VARCHAR(MAX),

Descricao VARCHAR(MAX)

)

INSERT @Tabela_Original (

Categoria,

Descricao

)

SELECT

Categoria,

Descricao

FROM

dbo.Teste_Group_Concat

ORDER BY

Categoria

DECLARE @Tabela TABLE (

Id INT IDENTITY(1, 1),

Categoria VARCHAR(MAX),

Descricoes VARCHAR(MAX)

)

INSERT @Tabela (

Categoria,

Descricoes

)

SELECT

Categoria,

FROM

dbo.Teste_Group_Concat

GROUP BY

Categoria

DECLARE

@Categoria VARCHAR(MAX),

@Descricao VARCHAR(MAX),

@Descricoes VARCHAR(MAX),

@Contador INT = 1,

@Numero_Linhas INT = (SELECT COUNT(*) FROM @Tabela_Original)

WHILE(@Contador <= @Numero_Linhas)

BEGIN

SELECT

@Categoria = ISNULL(Categoria, ''),

@Descricao = Descricao

FROM

@Tabela_Original

WHERE

Id = @Contador

ORDER BY

Categoria,

Descricao

UPDATE @Tabela

SET Descricoes += ', ' + @Descricao

WHERE ISNULL(Categoria, '') = ISNULL(@Categoria, '')

SET @Contador = @Contador + 1

END

SELECT

Categoria,

Descricoes = STUFF(Descricoes, 1, 1, '')

FROM

@Tabela

ORDER BY

Categoria

Solution served, but like all looping, it is not performative.

CTE RECURSIVE

How to concatenate columns in grouped strings using Recursive CTE

;WITH Dados as 
(
    SELECT 
        Categoria, 
        CONVERT(NVARCHAR(MAX), Descricao) AS Descricao,
        ROW_NUMBER() OVER (PARTITION BY Categoria ORDER BY Descricao) AS Linha
    FROM 
        dbo.Teste_Group_Concat
),
Tabela1 AS 
(
    SELECT Categoria, Descricao, Linha FROM Dados WHERE Linha = 1
),
Resultado AS
(
    SELECT Categoria, Descricao, Linha FROM Tabela1 WHERE Linha = 1
    
    UNION ALL

    SELECT Dados.Categoria, Resultado.Descricao + N', ' + Dados.Descricao, Dados.Linha
    FROM Dados 
    JOIN Resultado ON Resultado.Categoria = Dados.Categoria AND Dados.Linha = Resultado.Linha + 1
)
SELECT 
    Categoria, 
    Descricoes = MAX(Descricao)
FROM 
    Resultado
GROUP BY 
    Categoria 
ORDER BY 
    Categoria
OPTION (MAXRECURSION 0);

;WITH Dados as

(

SELECT

Categoria,

CONVERT(NVARCHAR(MAX), Descricao) AS Descricao,

ROW_NUMBER() OVER (PARTITION BY Categoria ORDER BY Descricao) AS Linha

FROM

dbo.Teste_Group_Concat

Tabela1 AS

(

SELECT Categoria, Descricao, Linha FROM Dados WHERE Linha = 1

Resultado AS

(

SELECT Categoria, Descricao, Linha FROM Tabela1 WHERE Linha = 1

UNION ALL

SELECT Dados.Categoria, Resultado.Descricao + N', ' + Dados.Descricao, Dados.Linha

FROM Dados

JOIN Resultado ON Resultado.Categoria = Dados.Categoria AND Dados.Linha = Resultado.Linha + 1

)

SELECT

Categoria,

Descricoes = MAX(Descricao)

FROM

Resultado

GROUP BY

Categoria

ORDER BY

Categoria

OPTION (MAXRECURSION 0);

This solution uses the recursion technique to solve our problem without looping. Although not very easy to understand at first, it is a practical and very interesting solution.

SCALAR FUNCTION (UDF)

How to Concatenate Columns in Grouped Strings Using Scalar Function (UDF)

CREATE FUNCTION dbo.fncConcatCategoria ( 
    @Ds_Categoria VARCHAR(MAX) 
)
RETURNS VARCHAR(MAX)
WITH SCHEMABINDING
AS
BEGIN

    DECLARE @Retorno VARCHAR(MAX);
 
    SELECT  
        @Retorno = COALESCE(@Retorno + ', ', '') + Descricao
    FROM
        dbo.Teste_Group_Concat
    WHERE
        ISNULL(Categoria, '') = ISNULL(@Ds_Categoria, '')
    ORDER BY 
        Descricao
 
    RETURN @Retorno

END
GO

SELECT 
    Categoria,
    dbo.fncConcatCategoria(Categoria) AS Descricao
FROM 
    dbo.Teste_Group_Concat
GROUP BY
    Categoria

CREATE FUNCTION dbo.fncConcatCategoria (

@Ds_Categoria VARCHAR(MAX)

)

RETURNS VARCHAR(MAX)

WITH SCHEMABINDING

BEGIN

DECLARE @Retorno VARCHAR(MAX);

SELECT

@Retorno = COALESCE(@Retorno + ', ', '') + Descricao

FROM

dbo.Teste_Group_Concat

WHERE

ISNULL(Categoria, '') = ISNULL(@Ds_Categoria, '')

ORDER BY

Descricao

RETURN @Retorno

END

SELECT

Categoria,

dbo.fncConcatCategoria(Categoria) AS Descricao

FROM

dbo.Teste_Group_Concat

GROUP BY

Categoria

Very useful function and once created, becomes very practical to use. The problem with this solution is that it is not very performative and requires you to create a function for each table that you need to perform this solution on, that is, it is not very generic and you would need to create several functions that do pretty much the same thing in your data base.

SQL CLR (C #)

How to concatenate columns in grouped strings using SCL CLR (C #)

using System;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Text;

[Serializable]
[SqlUserDefinedAggregate(
    Format.UserDefined,
    IsInvariantToNulls = false,
    IsInvariantToDuplicates = false,
    IsInvariantToOrder = true,
    MaxByteSize = -1)]
public struct concat : IBinarySerialize, INullable
{
    private StringBuilder _accumulator;
    private string _delimiter;

    public bool IsNull { get; private set; }

    public void Init()
    {
        _accumulator = new StringBuilder();
        _delimiter = string.Empty;
        this.IsNull = true;
    }

    public void Accumulate([SqlFacet(MaxSize = -1)]SqlString Value, [SqlFacet(MaxSize = -1)]SqlString Delimiter)
    {

        if (Value.IsNull) return;

        if (!Delimiter.IsNull & Delimiter.Value.Length > 0)
        {
            _delimiter = Delimiter.Value;
            if (_accumulator.Length > 0)
                _accumulator.Append(Delimiter.Value);

        }

        _accumulator.Append(Value.Value);
        IsNull = false;
    }
    
    public void Merge(concat Group)
    {
        if (_accumulator.Length > 0
            & Group._accumulator.Length > 0) _accumulator.Append(_delimiter);

        _accumulator.Append(Group._accumulator.ToString());

    }

    public SqlString Terminate()
    {
        return new SqlString(_accumulator.ToString());
    }

    void IBinarySerialize.Read(System.IO.BinaryReader r)
    {
        _delimiter = r.ReadString();
        _accumulator = new StringBuilder(r.ReadString());

        if (_accumulator.Length != 0) this.IsNull = false;
    }

    void IBinarySerialize.Write(System.IO.BinaryWriter w)
    {
        w.Write(_delimiter);
        w.Write(_accumulator.ToString());
    }
}

using System;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

using System.Text;

[Serializable]

[SqlUserDefinedAggregate(

Format.UserDefined,

IsInvariantToNulls = false,

IsInvariantToDuplicates = false,

IsInvariantToOrder = true,

MaxByteSize = -1)]

public struct concat : IBinarySerialize, INullable

{

private StringBuilder _accumulator;

private string _delimiter;

public bool IsNull { get; private set; }

public void Init()

{

_accumulator = new StringBuilder();

_delimiter = string.Empty;

this.IsNull = true;

}

public void Accumulate([SqlFacet(MaxSize = -1)]SqlString Value, [SqlFacet(MaxSize = -1)]SqlString Delimiter)

{

if (Value.IsNull) return;

if (!Delimiter.IsNull & Delimiter.Value.Length > 0)

{

_delimiter = Delimiter.Value;

if (_accumulator.Length > 0)

_accumulator.Append(Delimiter.Value);

}

_accumulator.Append(Value.Value);

IsNull = false;

}

public void Merge(concat Group)

{

if (_accumulator.Length > 0

& Group._accumulator.Length > 0) _accumulator.Append(_delimiter);

_accumulator.Append(Group._accumulator.ToString());

}

public SqlString Terminate()

{

return new SqlString(_accumulator.ToString());

}

void IBinarySerialize.Read(System.IO.BinaryReader r)

{

_delimiter = r.ReadString();

_accumulator = new StringBuilder(r.ReadString());

if (_accumulator.Length != 0) this.IsNull = false;

}

void IBinarySerialize.Write(System.IO.BinaryWriter w)

{

w.Write(_delimiter);

w.Write(_accumulator.ToString());

}

My favorite solution. Practical, extremely fast, generic and solves our problem. Not sure what CLR is or know, but not sure how to implement it in your database? Learn more by visiting my post Introduction to SQL Common Language Runtime (CLR) in SQL Server.

Performance Considerations

Let's now measure our solutions and find out which ones are the fastest and the slowest.

CLR

STUFF + FOR XML PATH

UPDATED

Recursive CTE

UDF scalar function

While loop

Cursor Loop

Right away we can eliminate the loopings, which were much worse. What happens if we insert more records? Like some 850.000 lines. What will the performance be like?

CLR

STUFF + FOR XML PATH

Since no other method was able to finish processing in less than 1 minute, although I used 850.000 lines with the CLR and FOR XML PATH, I will only use 158.000 lines (27%) for the rest of the methods to try to parse the results. We will see.

UPDATED

Until the time with UPDATE wasn't too bad. 5.7s to 158.000 lines is a reasonable time.

UDF scalar function

Recursive CTE

Well, I tried to wait for the Recursive CTE .. I even went to lunch and left running here, but after 2 hours and 22 minutes I couldn't wait to finish processing the 158 thousand lines (remembering that the CLR processed 850.000 in 3s and FOR XML in 1.5s) ..

Apparently our winner was FOR XML PATH, but if we are going to analyze the results, the CLR delivered the correct result, even with all this nonsense rows:

FOR XML PATH… It ended up getting lost and the results were not in the correct order.

Therefore, the best solution for this kind of situation is SQL CLR!

That's it folks!
Thanks for stopping by and see you in the next post.

sql server clr function stuff for xml path recursive cte convert columns rows grouped concat concatenation string how to convert concatenate columns to string

Concatenate many rows into single text string

André Soares Carvalho said:

21 February 2017 to 11: 15

Congratulations Dirceu, for sharing this valuable information, I take the opportunity to add a plugin to your topic that I found after your blog, with four functions already ready for the clr, just adding it to the bank.

http://groupconcat.codeplex.com/

- Dirceu Resende said:
  
  24 February 2017 to 06: 47
  
  André, thanks for the compliment and for sharing this link. I will take a look at it to learn more about.
  
Laércio Coelho said:

21 July 2016 to 16: 36

Thanks for the reply, Dirceu!

I didn't remember SQL Sentry anymore. I used a version a long time ago, but I don't think it was like that. I am already installing here to evaluate again.

Thanks a lot!

Laércio Coelho said:

21 July 2016 to 10: 39

Dirceu,

I would like to congratulate you on the article! Didactic and very practical, was calm to understand and compare the various solutions.
I have been particularly using the FOR XML with STUFF solution, which has served me well so far. But the SQL CLR solution was really good! Case to think for next implementations of this.

Just one question: did you use SQL Server or another database? In fact, I was wondering which tool you used in these graphical comparisons, which I thought was really cool.

Thank you!

Laércio

- Dirceu Resende said:
  
  21 July 2016 to 12: 26
  
  Laercio,
  Good afternoon.
  
  Thank you so much for visiting and feedback?
  
  About your question, the database is SQL Server yes, but the tool I use to analyze the execution plan is SQL Sentry Plan Explorer FREE (I will make a post about this tool in the future).
  
  In my opinion, this tool offers a better view of the data, as well as some features to manipulate the information that SQL Server Management Studio does not have, but would return something similar by Management Studio itself.
  
  If you have any questions, do not hesitate to ask.

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SQL Server - How to concatenate rows by grouping data by a column (Grouped concatenation)

How to concatenate columns in grouped strings using COALESCE

How to concatenate columns in grouped strings using STUFF + FOR XML PATH

How to concatenate columns in grouped strings using UPDATE

How to concatenate columns in grouped strings using LOOPING with CURSOR

How to concatenate columns in grouped strings using LOOPING with WHILE

How to concatenate columns in grouped strings using Recursive CTE

How to Concatenate Columns in Grouped Strings Using Scalar Function (UDF)

How to concatenate columns in grouped strings using SCL CLR (C #)

Performance Considerations

sql server clr function stuff for xml path recursive cte convert columns rows grouped concat concatenation string how to convert concatenate columns to string

Concatenate many rows into single text string

You may also like ...

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How to concatenate columns in grouped strings using COALESCE

How to concatenate columns in grouped strings using STUFF + FOR XML PATH

How to concatenate columns in grouped strings using UPDATE

How to concatenate columns in grouped strings using LOOPING with CURSOR

How to concatenate columns in grouped strings using LOOPING with WHILE

How to concatenate columns in grouped strings using Recursive CTE

How to Concatenate Columns in Grouped Strings Using Scalar Function (UDF)

How to concatenate columns in grouped strings using SCL CLR (C #)

Performance Considerations

sql server clr function stuff for xml path recursive cte convert columns rows grouped concat concatenation string how to convert concatenate columns to string

Concatenate many rows into single text string

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Comments

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