Łączenie PostgreSQL przy użyciu JSONB

16

Mam ten SQL:

CREATE TABLE test(id SERIAL PRIMARY KEY, data JSONB);

INSERT INTO test(data) VALUES
   ('{"parent":null,"children":[2,3]}'),
   ('{"parent":1,   "children":[4,5]}'),
   ('{"parent":1,   "children":[]}'),
   ('{"parent":2,   "children":[]}'),
   ('{"parent":2,   "children":[]}');

To dałoby:

 id |                 data                 
----+--------------------------------------
  1 | {"parent": null, "children": [2, 3]}
  2 | {"parent": 1, "children": [4, 5]}
  3 | {"parent": 1, "children": []}
  4 | {"parent": 2, "children": []}
  5 | {"parent": 2, "children": []}

Kiedy robisz normalny dla wielu, pokazywałby coś takiego:

SELECT * 
FROM test x1
  LEFT JOIN test x2
    ON x1.id = (x2.data->>'parent')::INT;
 id |                 data                 | id |               data                
----+--------------------------------------+----+-----------------------------------
  1 | {"parent": null, "children": [2, 3]} |  2 | {"parent": 1, "children": [4, 5]}
  1 | {"parent": null, "children": [2, 3]} |  3 | {"parent": 1, "children": []}
  2 | {"parent": 1, "children": [4, 5]}    |  4 | {"parent": 2, "children": []}
  2 | {"parent": 1, "children": [4, 5]}    |  5 | {"parent": 2, "children": []}
  5 | {"parent": 2, "children": []}        |    | 
  4 | {"parent": 2, "children": []}        |    | 
  3 | {"parent": 1, "children": []}        |    |

Jak dołączyć na podstawie dzieci (za pomocą LEFT JOINlub WHERE IN)? Próbowałem:

SELECT data->>'children' FROM test;
 ?column? 
----------
 [2, 3]
 [4, 5]
 []
 []
 []

SELECT json_array_elements((data->>'children')::TEXT) FROM t...
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

SELECT json_array_elements((data->>'children')::JSONB) FROM ...
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

SELECT json_to_record((data->>'children')::JSON) FROM test;
ERROR:  function returning record called in context that cannot accept type record
HINT:  Try calling the function in the FROM clause using a column definition list.

SELECT * FROM json_to_record((test.data->>'children')::JSON);
ERROR:  missing FROM-clause entry for table "test"
LINE 1: SELECT * FROM json_to_record((test.data->>'children')::JSON)...
postgresql join json postgresql-9.4 Kokizzu
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Odpowiedzi:

23

Byłoby to bardziej wydajne:

Z jsonoraz json_array_elements()na stronie 9.3

SELECT p.id AS p_id, p.data AS p_data
     , c.id AS c_id, c.data AS c_data
FROM   test p
LEFT   JOIN LATERAL json_array_elements(p.data->'children') pc(child) ON TRUE
LEFT   JOIN test c ON c.id = pc.child::text::int;

  • Użyj ->operatora zamiast ->>w odniesieniu do children. Tak, jak to masz, najpierw rzucisz json/ jsonb do, texta potem z powrotem na json.

  • Prostym sposobem na wywołanie funkcji powrotu do zestawu jest LEFT [OUTER] JOIN LATERAL. Obejmuje to wiersze bez dzieci. Aby je wykluczyć , zmień na składnię [INNER] JOIN LATERALlub CROSS JOIN- lub stenografię przecinkiem:

    , json_array_elements(p.data->'children') pc(child)

  • Unikanie zduplikowanych nazw kolumn w wyniku.

SQL Fiddle.

Z jsonba jsonb_array_elements()w pg 9.4

EXPLAIN 
SELECT p.id AS p_id, p.data AS p_data
     , c.id AS c_id, c.data AS c_data
FROM   test p
LEFT   JOIN LATERAL jsonb_array_elements(p.data->'children') pc(child) ON TRUE
LEFT   JOIN test c ON c.id = pc.child::text::int;
-------------------------------------------------------------------------------------------
 Hash Left Join  (cost=37.69..4826.24 rows=123000 width=72)
   Hash Cond: (((pc.child)::text)::integer = c.id)
   ->  Nested Loop Left Join  (cost=0.01..2482.31 rows=123000 width=68)
         ->  Seq Scan on test p  (cost=0.00..22.30 rows=1230 width=36)
         ->  Function Scan on jsonb_array_elements pc  (cost=0.01..1.01 rows=100 width=32)
   ->  Hash  (cost=22.30..22.30 rows=1230 width=36)
         ->  Seq Scan on test c  (cost=0.00..22.30 rows=1230 width=36)

Poza tym: znormalizowany projekt DB z podstawowymi typami danych byłby do tego znacznie bardziej wydajny.

Erwin Brandstetter
źródło
na 9.4rc1 daje:LINE 4: LEFT JOIN LATERAL json_array_elements(p.data->'children') ... ^ HINT: No function matches the given name and argument types. You might need to add explicit type casts.
Kokizzu
^jest na początkujson_array_elements
Kokizzu
1
oh mój zły, powinienem jsonb_zamiast tego użyć json_funkcji
Kokizzu
3

Nieważne, znalazłem drogę

SELECT *
 FROM ( SELECT *, json_array_elements((data->>'children')::JSON) child FROM test) x1
   LEFT JOIN test x2
    ON x1.child::TEXT::INT = x2.id
;

 id |                 data                 | child | id |               data
----+--------------------------------------+-------+----+-----------------------------------
  1 | {"parent": null, "children": [2, 3]} | 2     |  2 | {"parent": 1, "children": [4, 5]}
  1 | {"parent": null, "children": [2, 3]} | 3     |  3 | {"parent": 1, "children": []}
  2 | {"parent": 1, "children": [4, 5]}    | 4     |  4 | {"parent": 2, "children": []}
  2 | {"parent": 1, "children": [4, 5]}    | 5     |  5 | {"parent": 2, "children": []}

                                                QUERY PLAN                                                 
-----------------------------------------------------------------------------------------------------------
 Hash Left Join  (cost=37.67..4217.38 rows=123000 width=104)
   Hash Cond: ((((json_array_elements(((test.data ->> 'children'::text))::json)))::text)::integer = x2.id)
   ->  Seq Scan on test  (cost=0.00..643.45 rows=123000 width=36)
   ->  Hash  (cost=22.30..22.30 rows=1230 width=36)
         ->  Seq Scan on test x2  (cost=0.00..22.30 rows=1230 width=36)

lub 

SELECT *
 FROM test x1
    LEFT JOIN ( SELECT *, json_array_elements((data->>'children')::JSON) child FROM test) x2
    ON x1.id = x2.child::TEXT::INT
;

 id |                 data                 | id |                 data                 | child 
----+--------------------------------------+----+--------------------------------------+-------
  2 | {"parent": 1, "children": [4, 5]}    |  1 | {"parent": null, "children": [2, 3]} | 2
  3 | {"parent": 1, "children": []}        |  1 | {"parent": null, "children": [2, 3]} | 3
  4 | {"parent": 2, "children": []}        |  2 | {"parent": 1, "children": [4, 5]}    | 4
  5 | {"parent": 2, "children": []}        |  2 | {"parent": 1, "children": [4, 5]}    | 5
  1 | {"parent": null, "children": [2, 3]} |    |                                      | 

                                                QUERY PLAN                                                 
-----------------------------------------------------------------------------------------------------------
 Hash Right Join  (cost=37.67..4217.38 rows=123000 width=104)
   Hash Cond: ((((json_array_elements(((test.data ->> 'children'::text))::json)))::text)::integer = x1.id)
   ->  Seq Scan on test  (cost=0.00..643.45 rows=123000 width=36)
   ->  Hash  (cost=22.30..22.30 rows=1230 width=36)
         ->  Seq Scan on test x1  (cost=0.00..22.30 rows=1230 width=36)
Kokizzu
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