text: --json 指定key去排序 
  with a as (
  select 1 id , '{"grade":10,"gradeCode":"A","gradeName":"An"}'::json k union all 
  select 2 id , '{"grade":50,"gradeCode":"B","gradeName":"BN"}'::json j
  )
  select * from a 
  order by k->>'grade' desc   
  
  id    |k                                            
  ------|---------------------------------------------
       2|{"grade":50,"gradeCode":"B","gradeName":"BN"}
       1|{"grade":10,"gradeCode":"A","gradeName":"An"}
  