SQL Server 2019

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SELECT CONVERT(nvarchar(MAX),N'{
    "PRODUCT": {
        "0": "a1",
        "1": "a2",
        "2": "a3",
        "3": "a4"
    },
    "STOCK": {
        "0": 3.0,
        "1": 3.0,
        "2": 0.5,
        "3": 6.0
    },
    "SALES": {
        "0": 2487.0,
        "1": 1841.0,
        "2": 391.0,
        "3": 2732.0
    }
}') AS Response
INTO dbo.Api;
1 rows affected

SELECT P.[value] aS Product,
       St.[value] AS Stock,
       Sa.[value] AS Sales
FROM [dbo].[Api] a
     CROSS APPLY OPENJSON (a.Response, '$.PRODUCT') P
     CROSS APPLY  OPENJSON (a.Response, '$.STOCK') St
     CROSS APPLY  OPENJSON (a.Response, '$.SALES') Sa
WHERE P.[key] = St.[Key]
  AND St.[Key] = Sa.[Key];


Product
Stock
Sales


a1
3.0
2487.0

a2
3.0
1841.0

a3
0.5
391.0

a4
6.0
2732.0


DROP TABLE dbo.Api;