Postgres JSON as TEXT 无法访问所需数据答案

【问题标题】：Postgres JSON as TEXT cannot access the needed dataPostgres JSON as TEXT 无法访问所需数据
【发布时间】：2021-09-22 11:28:03
【问题描述】：

您好，我是一名新的数据工程师，所以我还在学习。我刚开始在一家公司工作，我注意到他们将来自 API 的数据作为 JSON 提供，但他们将其作为文本存储在 Postgres 中。我认为我可以将其转换为 JSON，然后尝试从列中访问我需要的数据，但是当我运行查询时，我将所有内容都作为空值，请在下面找到数据和查询的示例。任何帮助将不胜感激:)

[
  {
    "name": "Vorwurf",
    "value": "Geschwindigkeitsverstoß",
    "type": "DROPDOWN_LIST",
    "isDefault": true,
    "isRequired": false,
    "option": "Geschwindigkeitsverstoß, Rotlichtverstoß, Abstandsverstoß, Handyverstoß, Alkohol, Anderer Tatvorwurf"
  },
  {
    "name": "Schreiben erhalten?",
    "value": "No",
    "type": "CHECKBOX",
    "isDefault": true,
    "isRequired": false
  },
  {
    "name": "Besteht Rechtsschutzversicherung",
    "value": "Yes",
    "type": "CHECKBOX",
    "isDefault": true,
    "isRequired": true
  },
  {
    "name": "Welches Schreiben liegt vor?",
    "value": "Bußgeldbescheid",
    "type": "DROPDOWN_LIST",
    "isDefault": true,
    "isRequired": false,
    "option": "Bußgeldbescheid, Anhörungsbogen, Zeugenfragebogen, Kein Schreiben"
  },
  {
    "name": "Lead Nummer",
    "value": "GM00002153",
    "type": "TEXT",
    "isDefault": true,
    "isRequired": false
  },
  {
    "name": "URL zum vorliegenden Schreiben",
    "value": null,
    "type": "TEXT",
    "isDefault": true,
    "isRequired": false
  },
  {
    "name": "Angabe Website - Wie möchten Sie uns Ihre Unterlagen senden?",
    "type": "DROPDOWN_LIST",
    "isDefault": true,
    "isRequired": false,
    "option": "Fax, E-Mail, Unterlagen bereits hochgeladen"
  }
]

With t as (select cast(custom_fields as json)
from test.matters),
CF as (SELECT custom_fields ->> 'name' as "name",
       custom_fields ->> 'isDefault' as "isDefault", 
       custom_fields ->> 'isRequired' as "isRequired",
       custom_fields ->> 'option' as "option",
       custom_fields ->> 'groups' as "groups",
       custom_fields ->> 'practice_ids' as "practice_ids",
       custom_fields ->> 'value' as "value"
from t)
select * from CF

我也尝试像这样将文本转换为 json：

SELECT custom_fields::json->>'name' FROM test.matters_che

【问题讨论】：

标签： arrays json postgresql

【解决方案1】：

您的 JSON 值是一个数组，因此您需要取消嵌套数组（将每个元素变成一行）。 ->> 运算符不适用于数组，只能用于“常规”JSON 对象。

可以使用jsonb_array_elements() 将 JSON 对象数组取消嵌套到行中。如果要在 WHERE 子句中使用列表达式，则需要将查询包装在派生表（或公用表表达式）中

select *
from (
  SELECT cf.item ->> 'name' as "name",
         cf.item ->> 'isDefault' as "isDefault", 
         cf.item ->> 'isRequired' as "isRequired",
         cf.item ->> 'option' as "option",
         cf.item ->> 'groups' as "groups",
         cf.item ->> 'practice_ids' as "practice_ids",
         cf.item ->> 'value' as "value"
  from your_table t
    cross join jsonb_array_elements(t.custom_fields::jsonb) as cf(item)
 ) t
 WHERE name = '....'

Online Example

【讨论】：