SELECT UNION into a text[]

[Alexander Farber]

Good evening,

I am trying to SELECT ARRAY_AGG into an array from 2 tables.

But unfortunately here is what I get in PostgreSQL 10.5:

SELECT ARRAY_AGG(hashed)
               FROM words_nouns
               WHERE added > TO_TIMESTAMP(1539100913)
UNION
SELECT ARRAY_AGG(hashed)
                FROM words_verbs
                WHERE added > TO_TIMESTAMP(1539100913);
                      array_agg
-----------------------------------------------------
 {noun1,noun2,noun3}
 {verb1,verb2}

And thus I can not assign it to the _added variable in my custom function:

CREATE OR REPLACE FUNCTION words_get_added(
                in_visited integer,
                OUT out_json jsonb
        ) RETURNS jsonb AS
$func$
DECLARE
        _added text[];
BEGIN
        -- create array with words added to dictionary since in_visited
timestamp
        IF in_visited > 0 THEN
                _added := (
                        SELECT ARRAY_AGG(hashed)
                        FROM words_nouns
                        WHERE added > TO_TIMESTAMP(in_visited)
                        UNION
                        SELECT ARRAY_AGG(hashed)
                        FROM words_verbs
                        WHERE added > TO_TIMESTAMP(in_visited)
                );

                IF CARDINALITY(_added) > 0 THEN
                        out_json := jsonb_build_object('added', _added);
                END IF;
        END IF;
END

And the assignment results in the error message:

 www java[1082]: org.postgresql.util.PSQLException: ERROR: more than one
row returned by a subquery used as an expression|  Where: SQL statement
"SELECT (|                        SELECT ARRAY_AGG(hashed) |
        FROM words_nouns |                        WHERE added >
TO_TIMESTAMP(in_visited)|                        UNION|
    SELECT ARRAY_AGG(hashed) |                        FROM words_verbs |
                    WHERE added > TO_TIMESTAMP(in_visited)|
)"|PL/pgSQL function words_get_added(integer) line 7 at assignment

Please help me to modify my SELECT UNION so that I get just 1 row as result:

 {noun1,noun2,noun3,verb1,verb2}

Regards
Alex