select tt.id, tt.tag, tt.val from (
select 1  as id, 'quiz_id'     as tag, '20571' as val union all
select 2  as id, 'question_id' as tag, 38091 as val union all
select 3  as id, 'answer_val'  as tag, 10 as val union all
select 4  as id, 'answer_val'  as tag, 11 as val union all
select 5  as id, 'answer_val'  as tag, 12 as val union all
select 6  as id, 'answer_val'  as tag, 13 as val union all
select 7  as id, 'answer_val'  as tag, 14 as val union all
-- 
select 8  as id, 'question_id' as tag, 38092 as val union all
select 9  as id, 'answer_val'  as tag, 15 as val union all
select 10 as id, 'answer_val'  as tag, 16 as val union all
--
select 11 as id, 'question_id' as tag, 38093 as val union all
select 12 as id, 'answer_val'  as tag, 20 as val union all
select 13 as id, 'answer_val'  as tag, 21 as val ) tt

 [code=sql]
create table quiz_question_answers
(
    quiz_id         bigint,
    question_id     bigint,
    answer          int
)

insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38091, 10);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38091, 11);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38091, 12);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38091, 13);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38091, 14);

insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38092, 15);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38092, 16);

insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38093, 20);
insert into quiz_question_answers(quiz_id, question_id, answer) values (20571, 38093, 21);

insert into quiz_question_answers(quiz_id, question_id, answer)
select 
(select max(val) from stg_json_structure_my tt
 where tt.id<s.id
   and tag='quiz_id') as quiz_id,
(select max(val) from stg_json_structure_my tt
 where tt.id<s.id
   and tag='question_id') as question_id,
s.val
from stg_json_structure_my s
where tag = 'answer_val'
order by id