Resp.: text array accumulate to multidimensional text array

2008/10/14, Rainer Zaiss <r(dot)zaiss(at)free(dot)fr>:
>
> I would like to aggregate a text array into a multidimensional text array.
>
> Let us say I have one table with two collumns
>
> ID ARRAY
> A {"A1","B1","C1"}
> A {"A2","B2","C2"}
> B {"A3","B3","C3"}
>
> If I use a GROUP BY ID, I would like to receive following result:
>
> ID ARRAY
> A {{"A1","B1","C1"},{"A2","B2","C2"}}
> B {{"A3","B3","C3"}}
>
> I searched around but I didn't find any solution
>

Try:

bdteste=# CREATE OR REPLACE FUNCTION array_cat1(p1 anyarray, p2
anyarray) RETURNS anyarray AS $$
bdteste$# BEGIN
bdteste$# IF p1 = '{}'::text[] THEN
bdteste$# RETURN(ARRAY[p2]);
bdteste$# ELSE
bdteste$# RETURN(ARRAY_CAT(p1, p2));
bdteste$# END IF;
bdteste$# END;
bdteste$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
bdteste=# CREATE AGGREGATE array_accum3(anyarray)
(
sfunc = array_cat1,
stype = anyarray,
initcond = '{}'
);
CREATE AGGREGATE
bdteste=# CREATE TEMP TABLE foo(
bdteste(# id char(1),
bdteste(# a text[]);
CREATE TABLE
bdteste=# INSERT INTO foo VALUES('A', '{"A1","B1","C1"}');
INSERT 0 1
bdteste=# INSERT INTO foo VALUES('A', '{"A2","B2","C2"}');
INSERT 0 1
bdteste=# INSERT INTO foo VALUES('B', '{"A3","B3","C3"}');
INSERT 0 1
bdteste=# SELECT * FROM foo;
id | a
----+------------
A | {A1,B1,C1}
A | {A2,B2,C2}
B | {A3,B3,C3}
(3 registros)

bdteste=# SELECT id, array_accum3(a) FROM foo GROUP BY id;
id | array_accum3
----+-------------------------
B | {{A3,B3,C3}}
A | {{A1,B1,C1},{A2,B2,C2}}
(2 registros)

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