Postgres SQL中的`->>`和`->`有什么区别? [英] What is the difference between `->>` and `->` in Postgres SQL?

问题描述

在SQL中->>和->有什么区别?

What is the difference between ->> and -> in SQL?

在此线程中(检查字段是否以json类型存在列postgresql )，回答者基本上建议使用，

In this thread (Check if field exists in json type column postgresql), the answerer basically recommends using,

json->'attribute' is not null

而不是

json->>'attribute' is not null

为什么使用单箭头而不是双箭头?以我有限的经验，两者都做同样的事情.

Why use a single arrow instead of a double arrow? In my limited experience, both do the same thing.

推荐答案

->返回json(b)，而->>返回text:

with t (jo, ja) as (values
    ('{"a":"b"}'::jsonb,('[1,2]')::jsonb)
)
select
    pg_typeof(jo -> 'a'), pg_typeof(jo ->> 'a'),
    pg_typeof(ja -> 1), pg_typeof(ja ->> 1)
from t
;
 pg_typeof | pg_typeof | pg_typeof | pg_typeof 
-----------+-----------+-----------+-----------
 jsonb     | text      | jsonb     | text

这篇关于Postgres SQL中的`->>`和`->`有什么区别?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！