sql server - Build json with variable key / json_modify variable 2nd parameter -

suppose have

create schema tmp go  create table tmp.properties (   parentid uniqueidentifier not null,   propertyname nvarchar(20) not null,   propertyvalue nvarchar(100) null,    primary key (parentid,propertyname) ) go  create table tmp.fulldata (   parentid uniqueidentifier not null,   properties nvarchar(max) null,    primary key (parentid) ) go  declare @id1 uniqueidentifier = 'f1935d6a-d5a6-4fa1-acf4-ba3858804cec',         @id2 uniqueidentifier = 'f1935d6b-d5a6-4fa1-acf4-ba3858804cec'  insert tmp.properties values (@id1, 'firstname', 'luke'), (@id1, 'lastname', 'skywalker'), (@id2, 'firstname', 'han'), (@id2, 'lastname', 'solo') 

please consider that:

• properties dynamically created , cannot know in advance propertynames
• at moment parents table contains 1m , properties table contains 23m records

how can fill tmp.fulldata with:

parentid                             properties ------------------------------------ ------------------------------------------------ f1935d6a-d5a6-4fa1-acf4-ba3858804cec { "firstname": "luke", "lastname": "skywalker" } f1935d6b-d5a6-4fa1-acf4-ba3858804cec { "firstname": "han", "test1": "solo" } 

i tried

insert tmp.fulldata (parentid, properties) select distinct parentid, '{}' tmp.properties  update f set properties = json_modify(properties, 'append $.' + p.propertyname, p.propertyvalue) tmp.fulldata f cross join tmp.properties p 

but know/imagine

msg 13610, level 16, state 2, line 39 argument 2 of "json_modify" must string literal. 

any other option? in advance

skip update , insert directly tmp.fulldata:

insert tmp.fulldata (parentid, properties) select     parentid     ,'{'      + stuff((                  select ',' + '"' + propertyname + '":"' + propertyvalue + '"'                  tmp.properties                  a.parentid = p.parentid                  xml path(''), type              ).value('.', 'varchar(max)'), 1, 1, ''             ) + '}' properties tmp.properties p group parentid;