flatten JSON array into comma delimited list I am trying to construct a SELECT statement which will take a JSONB column in the following format: 

{
  "Cities": [
    {
      "Name": "Atlanta"
    },
    {
      "Name": "London"
    },
    {
      "Name": "New York"
    }
  ]
}


The output of the column result set needs to be in the following format:

Atlanta, London, New York


UPDATE

@a_horse_with_no_name's answer below is correct, but my requirements are actually a little more complicated than originally posted. I actually need to fit this select in to a larger (join) query as follows:

select eo.citydata.cities.names &lt;-- Flattened Comma delimited JSON Array
from orderline o 
join eventorders eo on eo.orderlineid = o.id
join events e on e.id = eo.eventid
where e.id = '123'


Clearly the answer provided will need to be modified in order for this to work and I'm struggling to figure out how to do it.
Unnest the array, then aggregate back:

select string_agg(city, ',')
from (
  select x.val -&gt;&gt; 'Name' as city
  from the_table t
     cross join jsonb_array_elements(t.the_column -&gt; 'Cities') as x(val)
) t;


If you have a bigger query, use that in a derived table: 

select string_agg(t2.city, ',')
from (
  select x.val -&gt;&gt; 'Name' as city
  from (
    select eo.citydata
    from orderline o 
      join eventorders eo on eo.orderlineid = o.id
      join events e on e.id = eo.eventid
    where e.id = 123
  ) t1
     cross join jsonb_array_elements(t1.citydata -&gt; 'Cities') as x(val)
) t2;




Alternatively - if you need that very often - you can create a function that does this:

create function get_element_list(p_value jsonb, p_keyname text)
  returns text
as 
$$ 
   select string_agg(x.val -&gt;&gt; p_keyname, ',')
   from jsonb_array_elements(p_value) as x(val);
$$
language sql;


Then you can use it like this:

select get_element_list(eo.citydata -&gt; 'Cities', 'Name')
from orderline o 
  join eventorders eo on eo.orderlineid = o.id
  join events e on e.id = eo.eventid
where e.id = 123;