etcd_fdw=# select value from test where key = 'key2';
 value
--------
 value2
(1 row)

etcd_fdw=# select value from test where key >= 'key2';
 value
--------
 value2
 value3
 value4
 value5
 value6
(5 rows)

etcd_fdw=# select value, key from test where key = 'key2';
 value  | key
--------+------
 value2 | key2
(1 row)

-- some inserts for example
INSERT INTO test(key, value) VALUES
('/gather/84', '{"foo":"bar"}'),
('/gather/85', '{"foo":"baz"}');
INSERT 0 2

-- Update referencing key and value
UPDATE test
SET key=key, value = value::jsonb || '{"gather_status":"active"}'::jsonb
WHERE key = '/gather/84';
UPDATE 1

-- Update referencing only value
UPDATE test
SET value = value::jsonb || '{"gather_status":"active"}'::jsonb
WHERE key = '/gather/84';
UPDATE 1

select * from test where key like '/gather%';
    key     |                   value
------------+-------------------------------------------
 /gather/84 | {"foo": "bar", "gather_status": "active"}
 /gather/85 | {"foo":"baz"}
(2 rows)

-- just a test local table
CREATE TABLE local_gather(id int8);
INSERT INTO local_gather VALUES (84), (85);
CREATE TABLE
INSERT 0 2

SELECT
    g.*,
    sh.value::jsonb ->> 'gather_status'
FROM local_gather g
LEFT JOIN (SELECT key, value FROM test) sh
    ON sh.key = '/gather/' || g.id;
 id | ?column?
----+----------
 84 | active
 85 |
(2 rows)