How to ignore few properties in SQL Server JSON value - sql

Question

I have a table which has a column with JSON data. Every JSON object in each column has many properties. I have another table which has property name not all but few.
What I need to do is to write a query to select JSON data from table but JSON should not contain properties which are there in the second table. For example, below is the jSON table.
Id Person
1 {FirstName:"test", LastName: "test", Email: "test#test.abc"}
2 {FirstName:"syx", LastName: "ave", Email: "yyeyd#test.abc"}
Second table with properties name:
ExclusionId ExcludedProperty
1 Email
Query should join these two table and output should be
Id Person
1 {FirstName:"test", LastName: "test"}
2 {FirstName:"syx", LastName: "ave"}

Answer 1

With corrected JSON, you can use JSON_MODIFY() and set the desired value to NULL
Example
Declare #YourTable Table ([Id] int,[Person] varchar(500))
Insert Into #YourTable Values
(1,'{"FirstName":"test", "LastName": "test", "Email": "test#test.abc"}')
,(2,'{"FirstName":"syx", "LastName": "ave", "Email": "yyeyd#test.abc"}')
Select A.ID
,NewValue = JSON_MODIFY([Person],'$.Email',null)
From #YourTable A
Returns
ID NewValue
1 {"FirstName":"test", "LastName": "test"}
2 {"FirstName":"syx", "LastName": "ave"}

Answer 2

This is a fully generic approach with no need for dynamic SQL:
--a mockup to simulate your issue
--credits to John Cappelletti for the mockup-code
DECLARE #YourTable TABLE (Id INT,Person NVARCHAR(500))
INSERT INTO #YourTable VALUES
(1,'{"FirstName":"test", "LastName": "test", "Email": "test#test.abc"}')
,(2,'{"FirstName":"syx", "LastName": "ave", "Email": "yyeyd#test.abc"}');
DECLARE #ExcludeProperties TABLE (Id INT,PropName VARCHAR(500))
INSERT INTO #ExcludeProperties VALUES (1,'Email');
--The query
WITH cte AS
(
SELECT t.Id
,JsonValues.[key] AS PropName
,JsonValues.[value] AS PropValue
FROM #YourTable t
CROSS APPLY OPENJSON(t.Person) jsonValues
WHERE JsonValues.[key] COLLATE Latin1_General_CI_AS NOT IN(SELECT excl.PropName COLLATE Latin1_General_CI_AS FROm #ExcludeProperties excl)
)
SELECT cte.Id
,CONCAT('{',
STUFF((
SELECT CONCAT(',"',cte2.PropName,'":"',cte2.PropValue,'"')
FROM cte cte2
WHERE cte2.Id=cte.Id
FOR XML PATH('')
),1,1,'')
,'}')
FROM cte
GROUP BY cte.Id;
The idea in short:
First we use a CTE to create a list of all properties within your JSON as EAV (Entity-Attribute-Value). With this its easy to get rid of all the attributes, where the name is found in your exclude table.
As we are not allowed to use a column's value as the output column's alias we can build the JSON with string-methods instead of a FOR JSON query.
First I use a GROUP BY to reduce the final output to one-row-per-Id, and the I use a correlated sub-query to build the JSON per Id from the corresponding EAVs.