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

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(dot)panchenko(at)postgrespro(dot)ru> 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='play' 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?

Regards
Alex