web-dev-qa-db-ja.com

JSONBを使用して結合するPostgreSQL

私はこのSQLを持っています：

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":[]}');

それは与えるでしょう：

 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": []}

通常の1対多の場合、次のようになります。

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": []}        |    |

子供に基づいて参加する方法（LEFT JOINまたはWHERE INを使用）私はもう試した：

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)...
postgresqljoinjsonpostgresql-9.4
16
Kokizzu

これはより効率的です：

9.3のjsonおよび json_array_elements() を使用

_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;_

  • childrenへの参照では、_->_ではなく_->>_演算子を使用します。あなたのやり方では、最初にjson/jsonbをtextにキャストし、次にjsonにキャストします。

  • セットを返す関数を呼び出すきれいな方法は_LEFT [OUTER] JOIN LATERAL_です。これには、子のない行が含まれます。それらを除外するには、_[INNER] JOIN LATERAL_または_CROSS JOIN_に変更するか、カンマを使用した省略構文：

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

  • 結果の列名の重複を回避します。

SQLフィドル

9.4ページのjsonbおよび jsonb_array_elements() を使用

_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)
_

余談：基本的なデータ型を持つ正規化されたDB設計は、これに対してwayより効率的です。

23
Erwin Brandstetter

気にしない、私は道を見つけた

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)

または

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)
3
Kokizzu