PostgreSQL array, recursion and more

MESH Data Tree:

example:
Hallux;A01.378.610.250.300.792.380

where:
A01 is Body Regions
A01.378 is Extremities
A01.378.610 is Lower Extremity
A01.378.610.250 is Foot
A01.378.610.250.300 is Forefoot, Human
A01.378.610.250.300.792 is Toes

CREATE OR REPLACE FUNCTION mesh_split(text) RETURNS text[]
AS $$
return [split('\.',$_[0])];
$$ LANGUAGE plperlu;

arancia=# select mesh_split('A01.378.610.250.300.792.380');
mesh_split
-------------------------------
{A01,378,610,250,300,792,380}
(1 row)

/*
Is it a real array?
If it is, why can I not use index to access its items?
*/

arancia=# select mesh_split('A01.378.610.250.300.792.380')[1];
ERROR: syntax error at or near "["
LINE 1: select mesh_split('A01.378.610.250.300.792.380')[1];
^
/*
but it is an array, it behaves as it is.
*/
arancia=> select array_length(mesh_split('A01.378.610.250.300.792.380'),1);
array_length
--------------
7
(1 row)

/* How to get access to its items then?
*/

Another problem related:

arancia=> select * from meshtree where code = ANY
mesh_split('A01.378.610.250.300.792.380');
ERROR: syntax error at or near "mesh_split"
LINE 1: select * from meshtree where code = ANY mesh_split('A01.378....
^

select * from meshtree,
unnest(mesh_split('A01.378.610.250.300.792.380')) as c where
c=meshtree.code;
parent | id | code | description

--------+-------+------+-------------------------------------------------------------------
10 | 11 | 300 | Dehydroepiandrosterone Sulfate
33 | 34 | 250 | Cymarine
48 | 49 | 250 | Cymarine
61 | 62 | 250 | Dihydrotachysterol
66 | 68 | 300 | Calcitriol
65 | 69 | 250 | Calcifediol
92 | 93 | 380 | Glycodeoxycholic Acid
98 | 99 | 250 | Finasteride
111 | 117 | 300 | Chenodeoxycholic Acid
145 | 146 | 300 | Dehydroepiandrosterone Sulfate
180 | 182 | 250 | Ethinyl Estradiol-Norgestrel Combination
190 | 191 | 250 | Desoximetasone
[..]
| 18638 | A01 | Body Regions
[..]
190 | 192 | 300 | Dexamethasone Isonicotinate
195 | 196 | 250 | Clobetasol
199 | 200 | 300 | Fluocinonide
206 | 207 | 250 | Diflucortolone
266 | 267 | 300 | Dexamethasone Isonicotinate
281 | 282 | 250 | Diflucortolone
290 | 293 | 250 | Dehydrocholesterols
305 | 306 | 250 | Dihydrotachysterol
312 | 314 | 300 | Calcitriol
311 | 315 | 250 | Calcifediol
320 | 321 | 250 | Cholestanol
328 | 330 | 300 | Calcitriol
[..]
52135 | 52136 | 250 | Eye Injuries
52136 | 52137 | 250 | Eye Burns
52149 | 52155 | 300 | Hematoma, Epidural, Cranial
52181 | 52196 | 300 | Gallbladder Emptying
52269 | 52277 | 300 | Caplan Syndrome
52360 | 52368 | 300 | Caplan Syndrome
52428 | 52442 | 380 | Hemothorax
52476 | 52491 | 610 | Pneumonia
52534 | 52535 | 380 | Legionnaires' Disease
(2204 rows)

I really want to write better similar query:

arancia=> with recursive t(id,parent,codeparts,idx,last,descriptions) as (
SELECT
id, parent, mesh_split('A01.378.610.250.300.792.380'), 1,
array_length(mesh_split('A01.378.610.250.300.792.380'),1),
ARRAY[description]
FROM meshtree WHERE code='A01'
UNION ALL
SELECT m.id, m.parent, t.codeparts, idx+1, last, descriptions ||
ARRAY[description]
FROM meshtree AS m JOIN t ON (t.id=m.parent)
WHERE idx<=last AND m.code=t.codeparts[idx+1])
SELECT t.* FROM t;
id | parent | codeparts | idx | last |
descriptions
-------+--------+-------------------------------+-----+------+--------...
18638 | | {A01,378,610,250,300,792,380} | 1 | 7 | {"Body
Regions"}
18675 | 18638 | {A01,378,610,250,300,792,380} | 2 | 7 | {"Body
Regions",Extremities}
18676 | 18675 | {A01,378,610,250,300,792,380} | 3 | 7 | {"Body
Regions",Extremities,"Lower Extremity"}
18679 | 18676 | {A01,378,610,250,300,792,380} | 4 | 7 | {"Body
Regions",Extremities,"Lower Extremity",Foot}
18682 | 18679 | {A01,378,610,250,300,792,380} | 5 | 7 | {"Body
Regions",Extremities,"Lower Extremity",Foot,"Forefoot, Human"}
18683 | 18682 | {A01,378,610,250,300,792,380} | 6 | 7 | {"Body
Regions",Extremities,"Lower Extremity",Foot,"Forefoot, Human",Toes}
18684 | 18683 | {A01,378,610,250,300,792,380} | 7 | 7 | {"Body
Regions",Extremities,"Lower Extremity",Foot,"Forefoot, Human",Toes,Hallux}
(7 rows)

explain analyze with recursive
t(id,parent,codeparts,idx,last,descriptions) as (
select
id,parent,mesh_split('A01.378.610.250.300.792.380'),1,array_length(mesh_split('A01.378.610.250.300.792.380'),1),ARRAY[description]
from meshtree where code='A01'
union all
select m.id,m.parent,t.codeparts,idx+1,last,descriptions ||
ARRAY[description] from meshtree as m join t on (t.id=m.parent) where
idx<=last and m.code=t.codeparts[idx+1]) select t.* from t;

QUERY PLAN

------------------------------------------------------------------------------------------------------------------------------------------------------
CTE Scan on t (cost=6336.53..6337.17 rows=32 width=80) (actual
time=4.850..9.453 rows=7 loops=1)
CTE t
-> Recursive Union (cost=0.00..6336.53 rows=32 width=99) (actual
time=4.839..9.397 rows=7 loops=1)
-> Index Scan using meshtree_id_code on meshtree
(cost=0.00..1030.38 rows=22 width=27) (actual time=4.828..8.895 rows=1
loops=1)
Index Cond: (code = 'A01'::text)
-> Nested Loop (cost=0.00..530.55 rows=1 width=99) (actual
time=0.051..0.061 rows=1 loops=7)
-> WorkTable Scan on t (cost=0.00..4.95 rows=73
width=76) (actual time=0.005..0.008 rows=1 loops=7)
Filter: (idx <= last)
-> Index Scan using meshtree_parent_code on meshtree
m (cost=0.00..7.18 rows=1 width=31) (actual time=0.031..0.034 rows=1
loops=7)
Index Cond: ((m.parent = t.id) AND (m.code =
t.codeparts[(t.idx + 1)]))
Total runtime: 9.758 ms
(11 rows)

PostgreSQL rocks!

Thank you in advance, \ferz