Hey guys,
Good afternoon.

In this post I will demonstrate how to read JSON strings and convert to a table and convert data from a table to JSON and XML using only T-SQL. This tip is very useful when you are using a version prior to SQL Server 2016 and need to read Json strings.

If you are using SQL Server 2016 or higher, be aware that there is already native support for JSON. To find out how this native support works, read my post SQL Server 2016 – Using native JSON support (JSON_VALUE, JSON_QUERY, OPENJSON, FOR JSON, ISJSON, JSON_MODIFY).

What is JSON

JSON, an acronym for “JavaScript Object Notation”, is a lightweight format for exchanging computational data. JSON's simplicity has resulted in its widespread use, especially as an alternative to XML in AJAX.

One of the claimed advantages of JSON over XML as a format for exchanging data in this context is the fact that it is much easier to write a JSON parser. In JavaScript itself, JSON can be trivially parsed using the eval() function. This was important for the acceptance of JSON within the AJAX community due to the presence of this JavaScript feature in all current web browsers.

In practice, arguments regarding ease of development and parser performance are rarely overlooked due to security concerns in using eval() and the increasing integration of XML processing in modern web browsers. For this reason JSON is typically used in environments where the size of the data stream between the client and server is of paramount importance (hence its use by Google, Yahoo, etc., which serve millions of users), where the source of the data can be explicitly trusted, and where the loss of client-side XSLT processing capabilities for data manipulation or interface generation is not a consideration.

A great use for using JSON in SQL Server and what motivated me to write this post, is for the integration and consumption of data from web services that use JSON to establish communication with the client consuming the information.

Reading a JSON string

Using the function I will post below, created by Phil Factor, it is possible to read JSON strings easily, as shown in the example below:

JSON1.1
JSON1.1

Implementing the function:
View source code

IF (OBJECT_ID (N'dbo.fncJSON_Read') IS NOT NULL) DROP FUNCTION dbo.fncJSON_Read
GO

CREATE FUNCTION dbo.fncJSON_Read ( 
    @JSON NVARCHAR(MAX) 
)
RETURNS @Retorno TABLE (
    Id_Elemento INT NULL,
    Nr_Sequencia [INT] NULL,
    Id_Objeto_Pai INT,
    Id_Objeto INT,
    Ds_Nome NVARCHAR(2000),
    Ds_String NVARCHAR(MAX) NOT NULL,
    Ds_Tipo VARCHAR(10) NOT NULL
)
AS
BEGIN


    DECLARE
        @FirstObject INT,
        @OpenDelimiter INT,
        @NextOpenDelimiter INT,
        @NextCloseDelimiter INT,
        @Type NVARCHAR(10),
        @NextCloseDelimiterChar CHAR(1),
        @Contents NVARCHAR(MAX),
        @Start INT,
        @end INT,
        @param INT,
        @EndOfDs_Nome INT,
        @token NVARCHAR(200),
        @value NVARCHAR(MAX),
        @Nr_Sequencia INT,
        @Ds_Nome NVARCHAR(200),
        @Id_Objeto_Pai INT,
        @lenJSON INT,
        @characters NCHAR(36),
        @result BIGINT,
        @index SMALLINT,
        @Escape INT
   
 
    DECLARE @Strings TABLE (
        String_ID INT IDENTITY(1, 1),
        Ds_String NVARCHAR(MAX)
    )
    
    SELECT
        @characters = '0123456789abcdefghijklmnopqrstuvwxyz',
        @Nr_Sequencia = 0,
        @Id_Objeto_Pai = 0;
        
    WHILE (1 = 1)
    BEGIN
    
        SELECT @Start = PATINDEX('%[^a-zA-Z]["]%', @JSON COLLATE SQL_Latin1_General_CP850_BIN);
        
        IF (@Start = 0)
            BREAK
            
        IF (SUBSTRING(@JSON, @Start + 1, 1) = '"')
        BEGIN
            SET @Start = @Start + 1;
            SET @end = PATINDEX('%[^\]["]%', RIGHT(@JSON, LEN(@JSON + '|') - @Start) COLLATE SQL_Latin1_General_CP850_BIN);
        END
        
        IF (@end = 0)
            BREAK
            
        SELECT
            @token = SUBSTRING(@JSON, @Start + 1, @end - 1)
      
      
        SELECT
            @token = REPLACE(@token, FromString, ToString)
        FROM (
              SELECT '\"' AS FromString, '"' AS ToString
              UNION ALL
              SELECT '\\', '\'
              UNION ALL
              SELECT '\/', '/'
              UNION ALL
              SELECT '\b', CHAR(08)
              UNION ALL
              SELECT '\f', CHAR(12)
              UNION ALL
              SELECT '\n', CHAR(10)
              UNION ALL
              SELECT '\r', CHAR(13)
              UNION ALL
              SELECT '\t', CHAR(09)
        ) substitutions
        
        
        SELECT
            @result = 0,
            @Escape = 1
  
  
        WHILE (@Escape > 0)
        BEGIN
        
            SELECT
                @index = 0,
                @Escape = PATINDEX('%\x[0-9a-f][0-9a-f][0-9a-f][0-9a-f]%', @token COLLATE SQL_Latin1_General_CP850_BIN)
                
                
            IF (@Escape > 0)
            BEGIN
            
                WHILE (@index < 4)
                BEGIN
                
                    SELECT
                        @result = @result + POWER(16, @index) * ( CHARINDEX(SUBSTRING(@token, @Escape + 2 + 3 - @index, 1), @characters) - 1 ),
                        @index = @index + 1;

                END
                      
                SELECT @token = STUFF(@token, @Escape, 6, NCHAR(@result))
                
            END
            
        END
      
      
        INSERT INTO @Strings ( Ds_String )
        SELECT @token
      
        
        SELECT @JSON = STUFF(@JSON, @Start, @end + 1, '@string' + CONVERT(NVARCHAR(5), @@IDENTITY))
        
    END
  
  
    WHILE (1 = 1)
    BEGIN
 
        SELECT @Id_Objeto_Pai = @Id_Objeto_Pai + 1
        SELECT @FirstObject = PATINDEX('%[{[[]%', @JSON COLLATE SQL_Latin1_General_CP850_BIN)
        
        IF (@FirstObject = 0)
            BREAK
            
            
        IF ( SUBSTRING(@JSON, @FirstObject, 1) = '{' )
            SELECT @NextCloseDelimiterChar = '}', @Type = 'object'
        ELSE
            SELECT @NextCloseDelimiterChar = ']', @Type = 'array'
            
             
        SELECT @OpenDelimiter = @FirstObject
 
 
        WHILE (1 = 1)
        BEGIN
        
            SELECT @lenJSON = LEN(@JSON + '|') - 1
            SELECT @NextCloseDelimiter = CHARINDEX(@NextCloseDelimiterChar, @JSON, @OpenDelimiter + 1)
            SELECT @NextOpenDelimiter = PATINDEX('%[{[[]%', RIGHT(@JSON, @lenJSON - @OpenDelimiter) COLLATE SQL_Latin1_General_CP850_BIN)
            
            
            IF (@NextOpenDelimiter = 0)
                BREAK
              
                
            SELECT @NextOpenDelimiter = @NextOpenDelimiter + @OpenDelimiter
            
            
            IF (@NextCloseDelimiter < @NextOpenDelimiter)
                BREAK
                
            
            IF SUBSTRING(@JSON, @NextOpenDelimiter, 1) = '{'
                SELECT @NextCloseDelimiterChar = '}', @Type = 'object'
            ELSE
                SELECT @NextCloseDelimiterChar = ']', @Type = 'array'

            
            SELECT @OpenDelimiter = @NextOpenDelimiter
            
            
        END
        
        
        SELECT @Contents = SUBSTRING(@JSON, @OpenDelimiter + 1, @NextCloseDelimiter - @OpenDelimiter - 1)
        SELECT @JSON = STUFF(@JSON, @OpenDelimiter, @NextCloseDelimiter - @OpenDelimiter + 1, '@' + @Type + CONVERT(NVARCHAR(5), @Id_Objeto_Pai))
        
        
        WHILE (( PATINDEX('%[A-Za-z0-9@+.e]%', @Contents COLLATE SQL_Latin1_General_CP850_BIN) ) <> 0)
        BEGIN
        
            IF (@Type = 'Object')
            BEGIN
                    
                SELECT 
                    @Nr_Sequencia = 0,
                    @end = CHARINDEX(':', ' ' + @Contents)
                    
                    
                SELECT @Start = PATINDEX('%[^A-Za-z@][@]%', ' ' + @Contents COLLATE SQL_Latin1_General_CP850_BIN)--AAAAAAAA
                    
                      
                SELECT
                    @token = SUBSTRING(' ' + @Contents, @Start + 1, @end - @Start - 1),
                    @EndOfDs_Nome = PATINDEX('%[0-9]%', @token COLLATE SQL_Latin1_General_CP850_BIN),
                    @param = RIGHT(@token, LEN(@token) - @EndOfDs_Nome + 1)
                    
                    
                SELECT
                    @token = LEFT(@token, @EndOfDs_Nome - 1),
                    @Contents = RIGHT(' ' + @Contents, LEN(' ' + @Contents + '|') - @end - 1)
                    
                    
                SELECT
                    @Ds_Nome = Ds_String
                FROM
                    @Strings
                WHERE
                    String_ID = @param
                    
                    
            END
            ELSE
                SELECT 
                    @Ds_Nome = NULL, 
                    @Nr_Sequencia = @Nr_Sequencia + 1
                    
                    
            SELECT @end = CHARINDEX(',', @Contents)
            
            
            IF (@end = 0)
                SELECT @end = PATINDEX('%[A-Za-z0-9@+.e][^A-Za-z0-9@+.e]%', @Contents + ' ' COLLATE SQL_Latin1_General_CP850_BIN) + 1
                
                
            SELECT @Start = PATINDEX('%[^A-Za-z0-9@+.e][A-Za-z0-9@+.e]%', ' ' + @Contents COLLATE SQL_Latin1_General_CP850_BIN)
      
      
            SELECT
                @value = RTRIM(SUBSTRING(@Contents, @Start, @end - @Start)),
                @Contents = RIGHT(@Contents + ' ', LEN(@Contents + '|') - @end)
                
                
            IF (SUBSTRING(@value, 1, 7) = '@object')
            BEGIN
            
                INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Id_Objeto, Ds_Tipo )
                SELECT
                    @Ds_Nome,
                    @Nr_Sequencia,
                    @Id_Objeto_Pai,
                    SUBSTRING(@value, 8, 5),
                    SUBSTRING(@value, 8, 5),
                    'object'
                    
            END
            ELSE BEGIN
            
                IF (SUBSTRING(@value, 1, 6) = '@array')
                
                    INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Id_Objeto, Ds_Tipo )
                    SELECT
                        @Ds_Nome,
                        @Nr_Sequencia,
                        @Id_Objeto_Pai,
                        SUBSTRING(@value, 7, 5),
                        SUBSTRING(@value, 7, 5),
                        'array'
                        
                ELSE
                
                    IF (SUBSTRING(@value, 1, 7) = '@string')
                        INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Ds_Tipo )
                        SELECT
                            @Ds_Nome,
                            @Nr_Sequencia,
                            @Id_Objeto_Pai,
                            Ds_String,
                            'string'
                         FROM
                            @Strings
                         WHERE
                            String_ID = SUBSTRING(@value, 8, 5)
                            
                    ELSE
                    
                         IF (@value IN ( 'true', 'false' ))
                            INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Ds_Tipo )
                            SELECT
                                @Ds_Nome,
                                @Nr_Sequencia,
                                @Id_Objeto_Pai,
                                @value,
                                'boolean'
                         ELSE
                         
                            IF (@value = 'null')
                                INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Ds_Tipo )
                                SELECT
                                    @Ds_Nome,
                                    @Nr_Sequencia,
                                    @Id_Objeto_Pai,
                                    @value,
                                    'null'
                                    
                            ELSE
                            
                                IF (PATINDEX('%[^0-9]%', @value COLLATE SQL_Latin1_General_CP850_BIN) > 0)
                                    INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Ds_Tipo )
                                    SELECT
                                        @Ds_Nome,
                                        @Nr_Sequencia,
                                        @Id_Objeto_Pai,
                                        @value,
                                        'real'
                                        
                                ELSE
                                
                                    INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Ds_Tipo )
                                    SELECT
                                        @Ds_Nome,
                                        @Nr_Sequencia,
                                        @Id_Objeto_Pai,
                                        @value,
                                        'int'
                                        
                IF (@Contents = ' ')
                    SELECT @Nr_Sequencia = 0
                    
            END
            
        END
        
    END
        
        
    INSERT INTO @Retorno ( Ds_Nome, Nr_Sequencia, Id_Objeto_Pai, Ds_String, Id_Objeto, Ds_Tipo )
    SELECT
        '-',
        1,
        NULL,
        '',
        @Id_Objeto_Pai - 1,
        @Type
        
        
    
    DECLARE @Tabela_Final TABLE (
        Id_Elemento INT IDENTITY(1, 1) NOT NULL,
        Nr_Sequencia [INT] NULL,
        Id_Objeto_Pai INT,
        Id_Objeto INT,
        Ds_Nome NVARCHAR(2000),
        Ds_String NVARCHAR(MAX) NOT NULL,
        Ds_Tipo VARCHAR(10) NOT NULL
    )
    
    INSERT INTO @Tabela_Final
    SELECT 
        Nr_Sequencia,
        Id_Objeto_Pai,
        Id_Objeto,
        Ds_Nome,
        Ds_String,
        Ds_Tipo 
    FROM
        @Retorno
    ORDER BY 
        ISNULL(Id_Objeto, Id_Objeto_Pai) DESC,
        Id_Objeto_Pai DESC,
        Id_Elemento
        
        
    DELETE FROM @Retorno
    
    
    INSERT INTO @Retorno
    SELECT
        Id_Elemento,
        Nr_Sequencia,
        Id_Objeto_Pai,
        Id_Objeto,
        Ds_Nome,
        Ds_String,
        Ds_Tipo 
    FROM 
        @Tabela_Final
    
        
    RETURN
    
    
END

Creating a JSON string from the database

Using this function, you can create a JSON string from a table in a specific format. To do this, we need to create this type of data before using our function.

Prerequisite – Creating the function to process the data:

IF (OBJECT_ID (N'dbo.fncJSON_Escape') IS NOT NULL) DROP FUNCTION dbo.fncJSON_Escape
GO

CREATE FUNCTION dbo.fncJSON_Escape ( 
    @Ds_String NVARCHAR(MAX) 
)
RETURNS NVARCHAR(MAX)
AS
BEGIN

    SELECT
        @Ds_String = REPLACE(@Ds_String, FromString, ToString)
    FROM
        (
          SELECT '\"' AS FromString, '"' AS ToString
          UNION ALL
          SELECT '\', '\\'
          UNION ALL
          SELECT '/', '\/'
          UNION ALL
          SELECT CHAR(08), '\b'
          UNION ALL
          SELECT CHAR(12), '\f'
          UNION ALL
          SELECT CHAR(10), '\n'
          UNION ALL
          SELECT CHAR(13), '\r'
          UNION ALL
          SELECT CHAR(09), '\t'
        ) substitutions

    RETURN @Ds_String

END

Prerequisite – Creating the JSON type:

IF EXISTS (SELECT * FROM sys.types WHERE name = 'JSON') DROP TYPE dbo.JSON
CREATE TYPE dbo.JSON AS TABLE (
    Id_Elemento INT NOT NULL,
    Nr_Sequencia [INT] NULL,
    Id_Objeto_Pai INT,
    Id_Objeto INT,
    Ds_Nome NVARCHAR(2000),
    Ds_String NVARCHAR(MAX) NOT NULL,
    Ds_Tipo VARCHAR(10) NOT NULL,
    PRIMARY KEY (Id_Elemento)
)

Implementing the function:
View source code

IF (OBJECT_ID (N'dbo.fncJSON_From_SQL') IS NOT NULL) DROP FUNCTION dbo.fncJSON_From_SQL
GO

CREATE FUNCTION dbo.fncJSON_From_SQL (
    @Tabela_Original JSON READONLY
)
RETURNS NVARCHAR(MAX)
AS
BEGIN


    DECLARE
        @JSON NVARCHAR(MAX),
        @NewJSON NVARCHAR(MAX),
        @Where INT,
        @ANumber INT,
        @notNumber INT,
        @indent INT,
        @ii INT,
        @CrLf CHAR(2)

      
    SELECT
        @CrLf = CHAR(13) + CHAR(10),
        @JSON = CASE Ds_Tipo
                  WHEN 'array' THEN +COALESCE('{' + @CrLf + '  "' + Ds_Nome + '" : ', '') + '['
                  ELSE '{'
                END + @CrLf + CASE WHEN Ds_Tipo = 'array' AND Ds_Nome IS NOT NULL THEN '  '
                                   ELSE ''
                              END + '@Object' + CONVERT(VARCHAR(5), Id_Objeto) + @CrLf + CASE Ds_Tipo
                                                                                           WHEN 'array' THEN CASE WHEN Ds_Nome IS NULL THEN ']'
                                                                                                                  ELSE '  ]' + @CrLf + '}' + @CrLf
                                                                                                             END
                                                                                           ELSE '}'
                                                                                         END
    FROM
        @Tabela_Original
    WHERE
        Id_Objeto_Pai IS NULL AND Ds_Tipo IN ( 'object', 'document', 'array' )


    SELECT
        @ii = 1000

    WHILE (@ii > 0)
    BEGIN

        SELECT
            @Where = PATINDEX('%[^[a-zA-Z0-9]@Object%', @JSON)

        IF @Where = 0
            BREAK

    
        SET @indent = CHARINDEX(CHAR(10) + CHAR(13), REVERSE(LEFT(@JSON, @Where)) + CHAR(10) + CHAR(13)) - 1
        SET @notNumber = PATINDEX('%[^0-9]%', RIGHT(@JSON, LEN(@JSON + '|') - @Where - 8) + ' ')
        SET @NewJSON = NULL

        SELECT
            @NewJSON = COALESCE(@NewJSON + ',' + @CrLf + SPACE(@indent), '') + CASE WHEN parent.Ds_Tipo = 'array' THEN ''
                                                                                    ELSE COALESCE('"' + TheRow.Ds_Nome + '" : ', '')
                                                                               END + CASE TheRow.Ds_Tipo
                                                                                       WHEN 'array' THEN '  [' + @CrLf + SPACE(@indent + 2) + '@Object' + CONVERT(VARCHAR(5), TheRow.[Id_Objeto]) + @CrLf + SPACE(@indent + 2) + ']'
                                                                                       WHEN 'object' THEN '  {' + @CrLf + SPACE(@indent + 2) + '@Object' + CONVERT(VARCHAR(5), TheRow.[Id_Objeto]) + @CrLf + SPACE(@indent + 2) + '}'
                                                                                       WHEN 'string' THEN '"' + dbo.fncJSON_Escape(TheRow.Ds_String) + '"'
                                                                                       ELSE TheRow.Ds_String
                                                                                     END
        FROM
            @Tabela_Original TheRow
            INNER JOIN @Tabela_Original Parent ON parent.Id_Elemento = TheRow.Id_Objeto_Pai
        WHERE
            TheRow.Id_Objeto_Pai = SUBSTRING(@JSON, @Where + 8, @notNumber - 1)


        SELECT
            @JSON = STUFF(@JSON, @Where + 1, 8 + @notNumber - 1, @NewJSON),
            @ii = @ii - 1

    END


    RETURN @JSON


END
GO

Creating XML from JSON

Using the function fncJSON_To_XML, you can create XML from a JSON string passed to the function, like the example below:

JSON2
JSON2

JSON3
JSON3

JSON4
JSON4

JSON5
JSON5

If you need help reading and manipulating data in XML objects using SQL Server, learn how to do this by reading my article SQL Server – How to read, import and export data from XML files.

Implementing the function:
View source code

IF (OBJECT_ID(N'dbo.fncJSON_To_XML') IS NOT NULL) DROP FUNCTION dbo.fncJSON_To_XML
GO

CREATE FUNCTION dbo.fncJSON_To_XML (
    @Tabela_Original JSON READONLY
)
RETURNS NVARCHAR(MAX)
AS
BEGIN

    DECLARE
        @XMLAsString NVARCHAR(MAX),
        @NewXML NVARCHAR(MAX),
        @Entities NVARCHAR(MAX),
        @Objects NVARCHAR(MAX),
        @Ds_Nome NVARCHAR(200),
        @Where INT,
        @ANumber INT,
        @notNumber INT,
        @indent INT,
        @CrLf CHAR(2)

      
    SELECT
        @CrLf = CHAR(13) + CHAR(10),
        @XMLAsString = '<?xml version="1.0" ?>

@Object' + CONVERT(VARCHAR(5), Id_Objeto) + '

'
    FROM
        @Tabela_Original
    WHERE
        Id_Objeto_Pai IS NULL AND Ds_Tipo IN ( 'object', 'array' )


    WHILE (1 = 1)
    BEGIN

        SELECT
            @Where = PATINDEX('%[^a-zA-Z0-9]@Object%', @XMLAsString)

        IF (@Where = 0)
            BREAK

    
        SET @indent = CHARINDEX(CHAR(10) + CHAR(13), REVERSE(LEFT(@XMLAsString, @Where)) + CHAR(10) + CHAR(13)) - 1
        SET @notNumber = PATINDEX('%[^0-9]%', RIGHT(@XMLAsString, LEN(@XMLAsString + '|') - @Where - 8) + ' ')
        SET @Entities = NULL


        SELECT
            @Entities = COALESCE(@Entities + ' ', ' ') + Ds_Nome + '="' + REPLACE(REPLACE(REPLACE(Ds_String, '<', '<'), '&', '&'), '>', '>') + '"'
        FROM
            @Tabela_Original
        WHERE
            Id_Objeto_Pai = SUBSTRING(@XMLAsString, @Where + 8, @notNumber - 1) 
            AND Ds_Tipo NOT IN ( 'array', 'object' )


        SELECT
            @Entities = COALESCE(@Entities, ''),
            @Objects = '',
            @Ds_Nome = CASE WHEN Ds_Nome = '-' THEN 'root'
                         ELSE Ds_Nome
                    END
        FROM
            @Tabela_Original
        WHERE
            [Id_Objeto] = SUBSTRING(@XMLAsString, @Where + 8, @notNumber - 1) 

    

        SELECT
            @Objects = @Objects + @CrLf + SPACE(@indent + 2) + '@Object' + CONVERT(VARCHAR(5), Id_Objeto)
        FROM
            @Tabela_Original
        WHERE
            Id_Objeto_Pai = SUBSTRING(@XMLAsString, @Where + 8, @notNumber - 1) 
            AND Ds_Tipo IN ( 'array', 'object' )


        IF (@Objects = '')
            SELECT @NewXML = '<' + COALESCE(@Ds_Nome, 'item') + @Entities + ' />'
        ELSE
            SELECT @NewXML = '<' + COALESCE(@Ds_Nome, 'item') + @Entities + '>' + @Objects + @CrLf + +SPACE(@indent) + '</' + COALESCE(@Ds_Nome, 'item') + '>'


        SELECT
            @XMLAsString = STUFF(@XMLAsString, @Where + 1, 8 + @notNumber - 1, @NewXML)


    END


    RETURN @XMLAsString


END

Workaround to convert a JSON string to XML

With the function below (written by Daniel Muchmacher), you can easily convert Json strings to an XML document, where you can use SQL Server to browser between nodes and read the data as per your need. This function is very useful for instances that are using a version prior to SQL Server 2016 (without native JSON support), but you need to use this feature.

If you need help reading and manipulating data in XML objects using SQL Server, learn how to do this by reading my article SQL Server – How to read, import and export data from XML files.

Example:

DECLARE @json VARCHAR(MAX) = '{
    "glossary": {
        "title": "example glossary",
		"GlossDiv": {
            "title": "S",
			"GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
					"SortAs": "SGML",
					"GlossTerm": "Standard Generalized Markup Language",
					"Acronym": "SGML",
					"Abbrev": "ISO 8879:1986",
					"GlossDef": {
                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
						"GlossSeeAlso": ["GML", "XML"]
                    },
					"GlossSee": "markup"
                }
            }
        }
    }
}'

SELECT dbo.fncJson2xml(@json)

Result:

Function source code
CREATE FUNCTION dbo.fncJson2xml (
    @json VARCHAR(MAX)
)
RETURNS XML
AS
BEGIN

    DECLARE
        @output VARCHAR(MAX),
        @key VARCHAR(MAX),
        @value VARCHAR(MAX),
        @recursion_counter INT,
        @offset INT,
        @nested BIT,
        @array BIT,
        @tab CHAR(1) = CHAR(9),
        @cr CHAR(1) = CHAR(13),
        @lf CHAR(1) = CHAR(10);

    SET @json=LTRIM(RTRIM( REPLACE(REPLACE(REPLACE(@json, @cr, ''), @lf, ''), @tab, '')));

    IF (LEFT(@json, 1)<>'{' OR RIGHT(@json, 1)<>'}')
        RETURN '';

    SET @json=LTRIM(RTRIM(SUBSTRING(@json, 2, LEN(@json)-2)));

    SELECT @output = '';

    WHILE (@json <> '') 
    BEGIN;

        IF (LEFT(@json, 1)<>'"')
            RETURN 'Expected quote (start of key name). Found "' + LEFT(@json, 1)+'"';

        SET @key=SUBSTRING(@json, 2, PATINDEX('%[^\\]"%', SUBSTRING(@json, 2, LEN(@json))+' "'))
        SET @json=LTRIM(SUBSTRING(@json, LEN(@key)+3, LEN(@json)));

        IF (LEFT(@json, 1)<>':')
            RETURN 'Expected ":" after key name, found "' + LEFT(@json, 1)+'"!';

        SET @json=LTRIM(SUBSTRING(@json, 2, LEN(@json)));

        IF (LEFT(@json, 1)='[')
            SELECT @array=1, @json=LTRIM(SUBSTRING(@json, 2, LEN(@json)));

        IF (@array IS NULL) 
            SET @array=0;

        WHILE (@array IS NOT NULL) 
        BEGIN

            SELECT @value=NULL, @nested=0;
            
            IF (@value IS NULL AND LEFT(@json, 1)='{') 
            BEGIN;

                SELECT @recursion_counter=1, @offset=1;

                WHILE (@recursion_counter<>0 AND @offset<LEN(@json)) 
                BEGIN
                    SET @offset=@offset+ PATINDEX('%[{}]%', SUBSTRING(@json, @offset+1, LEN(@json)));
                    SET @recursion_counter=@recursion_counter + (CASE SUBSTRING(@json, @offset, 1) WHEN '{' THEN 1 WHEN '}' THEN -1 END);
                END

                SET @value=CAST( dbo.fncJson2xml(LEFT(@json, @offset)) AS varchar(max));
                SET @json=SUBSTRING(@json, @offset+1, LEN(@json));
                SET @nested=1;

            END

            IF (@value IS NULL AND LEFT(@json, 2)='""')
                SELECT @value='', @json=LTRIM(SUBSTRING(@json, 3, LEN(@json)));

            IF (@value IS NULL AND LEFT(@json, 1)='"') 
            BEGIN
                SET @value=SUBSTRING(@json, 2, PATINDEX('%[^\\]"%', SUBSTRING(@json, 2, LEN(@json))+' "'));
                SET @json=LTRIM(SUBSTRING(@json, LEN(@value)+3, LEN(@json)));
            END

            IF (@value IS NULL AND LEFT(@json, 1)=',')
                SET @value='';

            IF (@value IS NULL) 
            BEGIN
                SET @value=LEFT(@json, PATINDEX('%[,}]%', REPLACE(@json, ']', '}')+'}')-1);
                SET @json=SUBSTRING(@json, LEN(@value)+1, LEN(@json));
            END;

            SET @output = @output + @lf + @cr + REPLICATE(@tab, @@NESTLEVEL-1)+ '<' + REPLACE(@key, '@', '') + '>'+ ISNULL(REPLACE( REPLACE(@value, '\"', '"'), '\\', '\'), '')+ (CASE WHEN @nested=1 THEN @lf+@cr+REPLICATE(@tab, @@NESTLEVEL-1) ELSE '' END) + '</' + REPLACE(@key, '@', '') + '>'

            IF (@array=0 AND @json <> '' AND LEFT(@json, 1) <> ',')
                RETURN @output+'Expected "," after value, found "'+ LEFT(@json, 1)+'"!';

            IF (@array=1 AND LEFT(@json, 1) NOT IN (',', ']'))
                RETURN @output+'In array, expected "]" or "," after '+ 'value, found "'+LEFT(@json, 1)+'"!';

            IF (@array=1 AND LEFT(@json, 1)=']') 
            BEGIN
                SET @array=NULL;
                SET @json=LTRIM(SUBSTRING(@json, 2, LEN(@json)));

                IF (LEFT(@json, 1) NOT IN ('', ',')) 
                BEGIN
                    RETURN 'Closed array, expected ","!';
                END
            END

            
            SET @json=LTRIM(SUBSTRING(@json, 2, LEN(@json)+1));
            IF (@array=0) SET @array=NULL;

        END;
    END;

    RETURN CAST(@output AS XML);

END;
GO

That's it.
Until the next post!