SQL Server - Using JSON to return Column Names

Question

I have the following test query I'm needing to make dynamic.

Basically a stored procedure will be passed @json and it needs to return the column names that are passed in that variable.

Is this possible and how could I do it?

declare @json varchar(max)

set @json = '["FirstName", "LastName","DOB"]';  

select *   
from OPENJSON( @json )  

select
FirstName,
LastName,
DOB
from Client

I do have this that works, but not sure on whether it's a good option and whether there's a better way

declare @json varchar(max)
declare @columnames varchar (200)
declare @sqlquery nvarchar(200)

set @json = '["FirstName", "LastName","DOB"]';  
set @columnames =''

select @columnames = 
    case when @columnames = ''
    then value
    else @columnames + coalesce(',' + value, '')
    end
  from OPENJSON( @json )  

set  @sqlquery = 'select ' + @columnames + ' from Client'

EXEC SP_EXECUTESQL @sqlquery

Basically the @json variable can contain one or many or all of the below fields and over-time even more.

set @json = '["FirstName", "LastName","DOB","DrugName,"Age","AgeGroup","Overdose","VerificationCode","Gender"]'; 

Answer 1

In this case (your json string contain only header with column names) and used for column selection only so it's easy. It's much more harder if you would like get values from json string too.

Variant 1: Use system table to validate your input and get column names.

declare @json varchar(800) = '["FirstName", "LastName", "DOB","DrugName,"Age","AgeGroup", "Overdose","VerificationCode","Gender"]',
@columnames varchar(800)

select @columnames = isnull(@sql + ', ', name) + name
from (
    select name, '"' + name + '"' name_quoted
    from sys.columns c
    where object_id('dbo.Client') = object_id) t
where @json like '%' + name_quoted + '%'

print @columnames
exec ('select ' + @columnames + ' from dbo.Client')

Variant 2: Working with strings.

declare @json varchar(800) = '["FirstName", "LastName","DOB","DrugName,"Age","AgeGroup","Overdose","VerificationCode","Gender"]';
declare @sql varchar(max) = replace(substring(@json, 2, len(@json) - 2), '"','')
print @sql
exec ('select ' + @sql + ' from dbo.Client')