array_agg for Array Types

Question

I\'m trying to get array_agg to work with an array type in Postgresql and I\'m having trouble figuring out if this is possible and if so how to do it. The perti

Answer 1

or cast the array to text like array_agg(array[xxx, yyy]::text)

array_agg(ARRAY[e.alert_type::text, e.id::text,
cast(extract(epoch from e.date_happened) as text)]::text
order by e.date_happened asc, e.id asc)

Answer 2

You could write custom aggregate to handle your specific array of arrays, e.g.:

DROP TABLE IF EXISTS e;
CREATE TABLE e
(
    id serial PRIMARY KEY,
    alert_type text,
    date_happened timestamp with time zone
);

INSERT INTO e(alert_type, date_happened) VALUES
    ('red', '2011-05-10 10:15:06'),
    ('yellow', '2011-06-22 20:01:19');

CREATE OR REPLACE FUNCTION array_agg_custom_cut(anyarray)
RETURNS anyarray
    AS 'SELECT $1[2:array_length($1, 1)]'
LANGUAGE SQL IMMUTABLE;

DROP AGGREGATE IF EXISTS array_agg_custom(anyarray);
CREATE AGGREGATE array_agg_custom(anyarray)
(
    SFUNC = array_cat,
    STYPE = anyarray,
    FINALFUNC = array_agg_custom_cut,
    INITCOND = $${{'', '', ''}}$$
);

Query:

SELECT
    array_agg_custom(
        ARRAY[
            alert_type::text,
            id::text,
            CAST(extract(epoch FROM date_happened) AS text)
        ])
FROM e;

Result:

              array_agg_custom              
--------------------------------------------
 {{red,1,1305036906},{yellow,2,1308787279}}
(1 row)

EDIT:

Here is second, shorter way (that is, you don't need array_agg_custom_cut function, but as you see additional ARRAY level is necessary in query):

CREATE AGGREGATE array_agg_custom(anyarray)
(
    SFUNC = array_cat,
    STYPE = anyarray
);

SELECT
    array_agg_custom(
        ARRAY[
            ARRAY[
                alert_type::text,
                id::text,
                CAST(extract(epoch FROM date_happened) AS text)
            ]
        ])
FROM e;

Result:

              array_agg_custom              
--------------------------------------------
 {{red,1,1305036906},{yellow,2,1308787279}}
(1 row)