postgres：如何在json_object_keys上实现类似json_agg的功能

Question

如果我想在单个查询中获取聚合在json数组中的json对象的键列表。这是我正在尝试的，它给了我一个错误：

Postgres版本：9.3

postgres=# create temporary table t_test ( 
postgres(# id integer,
postgres(# options json
postgres(# );
CREATE TABLE
postgres=# insert into t_test values (1, '{"x": 1, "y": 2}');
INSERT 0 1
postgres=# select * from t_test ;
 id |     options      
----+------------------
  1 | {"x": 1, "y": 2}
(1 row)

postgres=# select json_object_keys(options) from t_test ;
 json_object_keys 
------------------
 x
 y
(2 rows)

postgres=# select json_agg(json_object_keys(options)) from t_test ;
ERROR:  set-valued function called in context that cannot accept a set

Answer 1

select json_agg(o)
from (
    select json_object_keys(options) as o
    from t_test
) s
;
  json_agg  
------------
 ["x", "y"]