Converting JSON to table in SQL Server 2016

Question

I'm working on a Web project where the client application communicates with the DB via JSONs.

The initial implementation took place with SQL Server 2012 (NO JSON support and hence we implemented a Stored Function that handled the parsing) and now we are moving to 2016 (YES JSON support).

So far, we are reducing processing time by a significant factor (in some cases, over 200 times faster!).

There are some interactions that contain arrays that need to be converted into tables. To achieve that, the OPENJSON function does ALMOST what we need.

In some of these (array-based) cases, records within the arrays have one or more fields that are also OBJECTS (in this particular case, also arrays), for instance:

    [{
        "Formal_Round_Method": "Floor",
        "Public_Round_Method": "Closest",
        "Formal_Precision": "3",
        "Public_Precision": "3",
        "Formal_Significant_Digits": "3",
        "Public_Significant_Digits": "3",
        "General_Comment": [{
            "Timestamp": "2018-07-16 09:19",
            "From": "1",
            "Type": "Routine_Report",
            "Body": "[To + Media + What]: Comment 1",
            "$$hashKey": "object:1848"
        }, {
            "Timestamp": "2018-07-16 09:19",
            "From": "1",
            "Type": "User_Comment",
            "Body": "[]: Comment 2",
            "$$hashKey": "object:1857"
        }, {
            "Timestamp": "2018-07-16 09:19",
            "From": "1",
            "Type": "Routine_Report",
            "Body": "[To + Media + What]: Comment 3",
            "$$hashKey": "object:1862"
        }]
    }, {
        "Formal_Round_Method": "Floor",
        "Public_Round_Method": "Closest",
        "Formal_Precision": "3",
        "Public_Precision": "3",
        "Formal_Significant_Digits": "3",
        "Public_Significant_Digits": "3",
        "General_Comment": []

    }]

Here, General_Comment is also an array.

When running the command:

SELECT *
  FROM OPENJSON(@_l_Table_Data)
  WITH (    Formal_Round_Method                 NVARCHAR(16)    '$.Formal_Round_Method'               ,
            Public_Round_Method                 NVARCHAR(16)    '$.Public_Round_Method'               ,
            Formal_Precision                    INT             '$.Formal_Precision'                  ,
            Public_Precision                    INT             '$.Public_Precision'                  ,
            Formal_Significant_Digits           INT             '$.Formal_Significant_Digits'         ,
            Public_Significant_Digits           INT             '$.Public_Significant_Digits'         ,
            General_Comment                     NVARCHAR(4000)  '$.General_Comment'                   
        ) ;

[@_l_Table_Data is a variable holding the JSON string]

we are getting the column General_Comment = NULL even though the is data in there (at least in the first element of the array).

I guess that I should be using a different syntax for those columns that may contain OBJECTS and not SIMPLE VALUES, but I have no idea what that syntax should be.

Answer 1

I found a Microsoft page that actually solves the problem.

Here is how the query should look like:

SELECT *
  FROM OPENJSON(@_l_Table_Data)
  WITH (    Formal_Round_Method        NVARCHAR(16)    '$.Formal_Round_Method'               ,
            Public_Round_Method        NVARCHAR(16)    '$.Public_Round_Method'               ,
            Formal_Precision           INT             '$.Formal_Precision'                  ,
            Public_Precision           INT             '$.Public_Precision'                  ,
            Formal_Significant_Digits  INT             '$.Formal_Significant_Digits'         ,
            Public_Significant_Digits  INT             '$.Public_Significant_Digits'         ,
            General_Comment            NVARCHAR(MAX)   '$.General_Comment'   AS JSON                
    ) ;

So, you need to add AS JSON at the end of the column definition and (God knows why) the type MUST be NVARCHAR(MAX).

Very simple indeed!!!