sql - 在 PostgreSQL 中使用 json 数组中的索引

Question

引用original stackoverflow question ，我正在尝试将 gin 索引应用于 Postgres 9.4 中数组对象中的键，但我没有得到第一个答案中所述的结果。

你能纠正错误吗？

我遵循的步骤已写在下面。

第 1 部分:创建表和索引

CREATE TABLE tracks (id serial, artists jsonb);
CREATE INDEX tracks_artists_gin_idx ON tracks USING gin (artists);
INSERT INTO tracks (id, artists) VALUES (1, '[{"name": "blink-182"}]');
INSERT INTO tracks (id, artists) VALUES (2, '[{"name": "The Dirty Heads"}, {"name": "Louis Richards"}]');

第 2 部分:查询

SELECT * FROM tracks WHERE artists @> '{"name": "The Dirty Heads"}';
 id | artists 
----+---------
(0 rows)

此查询给出空结果。
我还尝试使用 jsonb_path_ops GIN 索引。

替代索引和查询:

DROP INDEX tracks_artists_gin_idx;
CREATE INDEX tracks_artistnames_gin_idx ON tracks USING  gin (artists jsonb_path_ops);
SELECT * FROM tracks WHERE artists @> '{"name": "The Dirty Heads"}';
 id | artists 
----+---------
(0 rows)

Answer 1

这个来自 original answer 的特定 jsonb 示例缺少包含查询的非原始对象周围的数组层 []。它已被修复。

为 PostgreSQL 9.4.x 记录的行为 jsonb Containment and Existence状态:

The general principle is that the contained object must match the containing object as to structure and data contents

...

As a special exception to the general principle that the structures must match, an array may contain a primitive value

特殊异常允许我们执行以下操作:

CREATE TABLE tracks (id serial, artistnames jsonb);
CREATE INDEX tracks_artistnames_gin_idx ON tracks USING gin (artistnames);
INSERT INTO tracks (id, artists) VALUES (1, '["blink-182"]');
INSERT INTO tracks (id, artists) VALUES (2, '["The Dirty Heads", "Louis Richards"]');

我们可以使用一般原则查询包含:

SELECT * FROM tracks WHERE artistnames @> '["The Dirty Heads"]';
 id |              artistnames              
----+---------------------------------------
  2 | ["The Dirty Heads", "Louis Richards"]
(1 row)

我们还可以使用特殊异常查询包含，因为数组包含基本类型:

SELECT * FROM tracks WHERE artistnames @> '"The Dirty Heads"';
 id |              artistnames              
----+---------------------------------------
  2 | ["The Dirty Heads", "Louis Richards"]
(1 row)

有 4 种基本类型允许对数组进行包含和存在查询:

1. 字符串
2. 人数
3. bool 值
4. 无

由于您在问题中提到的示例是处理嵌套在数组中的对象，因此我们不符合上述特殊异常(exception)的条件:

CREATE TABLE tracks (id serial, artists jsonb);
CREATE INDEX tracks_artists_gin_idx ON tracks USING gin (artists);
INSERT INTO tracks (id, artists) VALUES (1, '[{"name": "blink-182"}]');
INSERT INTO tracks (id, artists) VALUES (2, '[{"name": "The Dirty Heads"}, {"name": "Louis Richards"}]');

我们可以使用一般原则查询包含:

SELECT * FROM tracks WHERE artists @> '[{"name": "The Dirty Heads"}]';
 id |                          artists                          
----+-----------------------------------------------------------
  2 | [{"name": "The Dirty Heads"}, {"name": "Louis Richards"}]
(1 row)

对象不被视为原始类型，因此以下包含查询不符合特殊异常的条件，因此不起作用:

SELECT * FROM tracks WHERE artists @> '{"name": "The Dirty Heads"}';
 id | artists 
----+---------
(0 rows)