How do I ORDER BY a JSON Array with its String Values?

I have a simple JSON array:

_bb jsonb =

[
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "FlashSale",
    "pos": "Bottom"
  },
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  }
]

What I want to achieve:

[
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "FlashSale",
    "pos": "Bottom"
  }
]

I tried doing

Select _bb  into _test  ORDER BY _bb->>'pos' ASC  ;

What I achieve is all the pos = "Top" be the first in the JSON and all the "Bottom" to be last. Is there a way to achieve this in Postgres?

Solution

with j(_bb) as (values('[
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "FlashSale",
    "pos": "Bottom"
  },
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  }
]'::jsonb))
, ord(o,v) as (values(1,'Top'),(2,'Bottom'))
, un as (select *,jsonb_array_elements(_bb) i from j)
select jsonb_agg(i order by o) from un
join ord on v=i->>'pos'
;

with result in:

[
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "Testing",
    "pos": "Top"
  },
  {
    "so": "1",
    "mdl": "FlashSale",
    "pos": "Bottom"
  }
]

needless to say you have to build order matrix for all values, eg:

, ord(o,v) as (values(1,'Top'),(2,'Middle'),(3,'Bottom'))

http://rextester.com/ZNDQ97753