检查Postgres JSON数组是否包含字符串 [英] Check if a Postgres JSON array contains a string

问题描述

我有一张桌子来存储有关我的兔子的信息.看起来像这样:

I have a table to store information about my rabbits. It looks like this:

create table rabbits (rabbit_id bigserial primary key, info json not null);
insert into rabbits (info) values
  ('{"name":"Henry", "food":["lettuce","carrots"]}'),
  ('{"name":"Herald","food":["carrots","zucchini"]}'),
  ('{"name":"Helen", "food":["lettuce","cheese"]}');

我该如何找到喜欢胡萝卜的兔子?我想到了这个:

How should I find the rabbits who like carrots? I came up with this:

select info->>'name' from rabbits where exists (
  select 1 from json_array_elements(info->'food') as food
  where food::text = '"carrots"'
);

我不喜欢该查询.真是一团糟.

I don't like that query. It's a mess.

作为专职兔子管理员，我没有时间更改数据库架构.我只想适当地喂兔子.有没有更可读的方法来执行该查询?

As a full-time rabbit-keeper, I don't have time to change my database schema. I just want to properly feed my rabbits. Is there a more readable way to do that query?

推荐答案

从PostgreSQL 9.4开始，您可以使用

As of PostgreSQL 9.4, you can use the ? operator:

select info->>'name' from rabbits where (info->'food')::jsonb ? 'carrots';

如果您改为使用 jsonb 类型，甚至可以在"food"键上为?查询建立索引:

You can even index the ? query on the "food" key if you switch to the jsonb type instead:

alter table rabbits alter info type jsonb using info::jsonb;
create index on rabbits using gin ((info->'food'));
select info->>'name' from rabbits where info->'food' ? 'carrots';

当然，您可能没有时间担任专职兔子饲养员.

Of course, you probably don't have time for that as a full-time rabbit keeper.

更新:这是在一张1,000,000只兔子的桌子上性能改进的演示，其中每只兔子喜欢两种食物，其中10％像胡萝卜:

Update: Here's a demonstration of the performance improvements on a table of 1,000,000 rabbits where each rabbit likes two foods and 10% of them like carrots:

d=# -- Postgres 9.3 solution
d=# explain analyze select info->>'name' from rabbits where exists (
d(# select 1 from json_array_elements(info->'food') as food
d(#   where food::text = '"carrots"'
d(# );
 Execution time: 3084.927 ms

d=# -- Postgres 9.4+ solution
d=# explain analyze select info->'name' from rabbits where (info->'food')::jsonb ? 'carrots';
 Execution time: 1255.501 ms

d=# alter table rabbits alter info type jsonb using info::jsonb;
d=# explain analyze select info->'name' from rabbits where info->'food' ? 'carrots';
 Execution time: 465.919 ms

d=# create index on rabbits using gin ((info->'food'));
d=# explain analyze select info->'name' from rabbits where info->'food' ? 'carrots';
 Execution time: 256.478 ms

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