Re: Extract elements from JSON array and return them as concatenated string

["Ivan E. Panchenko" <i.panchenko@xxxxxxxxxxxxxx>]

14.03.2018 20:02, Alexander Farber пишет:

Thank you, Ivan! I am trying to apply your suggestion to my table -

On Wed, Mar 14, 2018 at 5:34 PM, Ivan E. Panchenko <i.panchenko@xxxxxxxxxxxxxx> wrote:

Hi Alex,

SELECT  string_agg(x->>'letter','') FROM json_array_elements(

'[{"col": 7, "row": 12, "value": 3, "letter": "A"}, {"col": 8, "row": 12, "value": 10, "letter": "B"}, {"col": 9, "row": 12, "value": 1, "letter": "C"}, {"col": 10, "row": 12, "value": 2, "letter": "D"}]'::json

) x;

# select * from words_moves where gid=656 order by played desc limit 3;
 mid  | action | gid | uid  |            played             |                                                tiles                                                 | score
------+--------+-----+------+-------------------------------+------------------------------------------------------------------------------------------------------+-------
 1353 | swap   | 656 |    7 | 2018-03-14 17:22:18.430082+01 | "ЙНРР"                                                                                               |     ¤
 1352 | play   | 656 | 1199 | 2018-03-14 16:55:45.898379+01 | [{"col": 4, "row": 7, "value": 2, "letter": "С"}, {"col": 5, "row": 7, "value": 3, "letter": "У"}]   |    19
 1351 | play   | 656 |    7 | 2018-03-14 16:38:48.132546+01 | [{"col": 9, "row": 11, "value": 5, "letter": "Ж"}, {"col": 9, "row": 13, "value": 2, "letter": "М"}] |    16
(3 rows)
 

by trying the following:

#  select string_agg(x->>'letter', ' ') from (select jsonb_array_elements(tiles) from words_moves where gid=656 and action='' order by played desc limit 5) x;
ERROR:  42883: operator does not exist: record ->> unknown
LINE 1: select string_agg(x->>'letter', ' ') from (select jsonb_arra...
                           ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
LOCATION:  op_error, parse_oper.c:728

I am probably missing something obvious?

Yes, here x is the alias for the record, not for the json field. So you need to write the query like

select string_agg(x->>'letter', ' ')
from (
   select jsonb_array_elements(tiles) x
   from words_moves
   where gid=656 and action=''
   order by played desc limit 5
) y;

Regards

Alex

Regards,
Ivan