SQL Server : query columns to JSON object with group by

Try this:

SELECT (SELECT [ID], [Keys], [ValueV]  FOR JSON PATH)
FROM #Test 
GROUP BY ID, keys, ValueV

or this:

SELECT (SELECT [ID], [Keys], [ValueV]  FOR JSON PATH, WITHOUT_ARRAY_WRAPPER)
FROM #Test 
GROUP BY ID, keys, ValueV

This works (in SQL Server 2017, where STRING_AGG is available), but is quite clumsy. I'm not sure there's not a more elegant way.

SELECT (
    SELECT 
       ID, 
       ValueV, 
       Keys = JSON_QUERY('["' + STRING_AGG(STRING_ESCAPE(Keys, 'json'), '","') + '"]')
    FOR JSON PATH
)
FROM #Test 
GROUP BY ID, ValueV

For SQL Server 2016 (which has no STRING_AGG, or STRING_ESCAPE for that matter):

SELECT (
    SELECT ID, ValueV, Keys = JSON_QUERY(REPLACE(REPLACE(
        (
            SELECT Keys 
            FROM #Test t2 WHERE t2.ID = t1.ID AND t2.ValueV = t1.ValueV 
            FOR JSON PATH
        ),
        '{"Keys":', ''),
        '}', ''))
    FOR JSON PATH
)
FROM #Test t1
GROUP BY ID, ValueV

Even less elegant, but you take what you can get. At least we're not concatenating with FOR XML...

Posting this if any one has the same sort of use case

SELECT [t].[ID], 
(SELECT [t1].[KEYS], [t1].[ValueV] FROM @Test t1 WHERE t1.[ID] = [t].id FOR JSON PATH ) a
FROM @Test AS [t]
GROUP BY [t].[ID]