SQL Server 2022

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-- https://stackoverflow.com/a/74713776/4709762

DECLARE @vJSON NVARCHAR(MAX) = N'{"a":1, "b":2, "c":3}'
DECLARE @vJSON2 NVARCHAR(MAX) = N'{"d":4, "e":5}'

SELECT
    @vJSON = JSON_MODIFY(@vJSON, CONCAT(N'$.', [Key]), value)
FROM
OPENJSON(@vJSON2)

SELECT @vJSON


(No column name)


{"a":1, "b":2, "c":3,"d":"4","e":"5"}


-- https://dba.stackexchange.com/q/332047/68127

DECLARE @FirstJSON NVARCHAR(MAX) = N'
{
    "message id": "B673A8E4-3652-4544-A02D-BA9726BD71ED",
    "volgnummer": 61000233530024,
    "debug": null,
    "kenmerken": {
        "item 1": 1,
        "item 2": 1,
        "item 3": 1
    }
}
';

DECLARE @KenmerkenToAdd NVARCHAR(MAX) = N'
{
    "Item 4": false,
    "Item 5": false
}
';

DECLARE @Kenmerken NVARCHAR(MAX) = JSON_QUERY(@FirstJSON,' $.kenmerken');
SELECT 
  @Kenmerken as Original, 
  @KenmerkenToAdd as Supplement;

SELECT @Kenmerken = JSON_MODIFY(
    @Kenmerken, 
    CONCAT(N'$.', QUOTENAME([key],'"')), 
    [value]
  )
FROM OPENJSON(@KenmerkenToAdd);

SELECT @Kenmerken as UnionSet;

SET @FirstJSON = JSON_MODIFY(
                               @FirstJSON,
                               ' $.kenmerken',
                               JSON_QUERY(@Kenmerken)
                            );

SELECT @FirstJSON as FinalJson;


Original
Supplement


{
        "item 1": 1,
        "item 2": 1,
        "item 3": 1
    }

{
    "Item 4": false,
    "Item 5": false
}





UnionSet


{
        "item 1": 1,
        "item 2": 1,
        "item 3": 1
    ,"Item 4":"false","Item 5":"false"}




FinalJson



{
    "message id": "B673A8E4-3652-4544-A02D-BA9726BD71ED",
    "volgnummer": 61000233530024,
    "debug": null,
    "kenmerken": {
        "item 1": 1,
        "item 2": 1,
        "item 3": 1
    ,"Item 4":"false","Item 5":"false"}
}



  