Converting JSON to table in SQL Server 2016 - json

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!!!

Answer 2

Create Function ParseJson:
Create or Alter FUNCTION [dbo].[ParseJson] (#JSON NVARCHAR(MAX))
RETURNS #Unwrapped TABLE
(
[id] INT IDENTITY, --just used to get a unique reference to each json item
[level] INT, --the hierarchy level
[key] NVARCHAR(100), --the key or name of the item
[Value] NVARCHAR(MAX),--the value, if it is a null, int,binary,numeric or string
type INT, --0 TO 5, the JSON type, null, numeric, string, binary, array or object
SQLDatatype sysname, --whatever the datatype can be parsed to
parent INT, --the ID of the parent
[path] NVARCHAR(4000) --the path as used by OpenJSON
)
AS begin
INSERT INTO #Unwrapped ([level], [key], Value, type, SQLDatatype, parent,
[path])
VALUES
(0, --the level
NULL, --the key,
#json, --the value,
CASE WHEN Left(ltrim(#json),1)='[' THEN 4 ELSE 5 END, --the type
'json', --SQLDataType,
0 , --no parent
'$' --base path
);
DECLARE #ii INT = 0,--the level
#Rowcount INT = -1; --the number of rows from the previous iteration
WHILE #Rowcount <> 0 --while we are still finding levels
BEGIN
INSERT INTO #Unwrapped ([level], [key], Value, type, SQLDatatype, parent,
[path])
SELECT [level] + 1 AS [level], new.[Key] AS [key],
new.[Value] AS [value], new.[Type] AS [type],
-- SQL Prompt formatting off
/* in order to determine the datatype of a json value, the best approach is to a determine
the datatype that can be parsed. It JSON, an array of objects can contain attributes that arent
consistent either in their name or value. */
CASE
WHEN new.Type = 0 THEN 'bit null'
WHEN new.[type] IN (1,2) then COALESCE(
CASE WHEN TRY_CONVERT(INT,new.[value]) IS NOT NULL THEN 'int' END,
CASE WHEN TRY_CONVERT(NUMERIC(14,4),new.[value]) IS NOT NULL THEN 'numeric' END,
CASE WHEN TRY_CONVERT(FLOAT,new.[value]) IS NOT NULL THEN 'float' END,
CASE WHEN TRY_CONVERT(MONEY,new.[value]) IS NOT NULL THEN 'money' END,
CASE WHEN TRY_CONVERT(DateTime,new.[value],126) IS NOT NULL THEN 'Datetime2' END,
CASE WHEN TRY_CONVERT(Datetime,new.[value],127) IS NOT NULL THEN 'Datetime2' END,
'nvarchar')
WHEN new.Type = 3 THEN 'bit'
WHEN new.Type = 5 THEN 'object' ELSE 'array' END AS SQLDatatype,
old.[id],
old.[path] + CASE WHEN old.type = 5 THEN '.' + new.[Key]
ELSE '[' + new.[Key] COLLATE DATABASE_DEFAULT + ']' END AS path
-- SQL Prompt formatting on
FROM #Unwrapped old
CROSS APPLY OpenJson(old.[Value]) new
WHERE old.[level] = #ii AND old.type IN (4, 5);
SELECT #Rowcount = ##RowCount;
SELECT #ii = #ii + 1;
END;
return
END
For Usage:
select * from ParseJson(jsonString)