如何通过SQL查询父子项以获取特定的JSON格式? [英] How to SQL query parent-child for specific JSON format?

问题描述

我期望我的jQuery代码使用此JSON:

{
  "projects": [
    {
      "id": "1",
      "project_name": "Carmichael House",
      "parent_id": "0",
      "children": [
        {
          "id": "2",
          "project_name": "Carmichael Kitchen",
          "parent_id": "1"
        },
        {
          "id": "3",
          "project_name": "Carmichael Bathroom",
          "parent_id": "1"
        }
      ]
    },
    {
      "id": "2",
      "project_name": "Dowd Apartment",
      "parent_id": "0",
      "children": [
        {
          "id": "4",
          "project_name": "Dowd Kitchen",
          "parent_id": "2"
        }
      ]
    }
  ]
}

此数据将来自MySql表 tbl_projects :

id
project_name
parent_id

SQL SELECT查询应该是什么，以便输出 1个平面表，可以轻松地将其转换为JSON(在PHP或JavaScript/jQuery中)?

我什至以正确的方式走这条路吗?

解决方案

您可以直接从MySQL生成JSON内容.这是可与MySQL 5.7或更高版本配合使用的解决方案.

首先，请考虑函数JSON_OBJECT() ，它为表中的每个记录生成一个JSON对象:

SELECT 
    p.*, 
    JSON_OBJECT('id', id, 'project_name', project_name, 'parent_id', parent_id) js
FROM tbl_projects p;

给出示例数据，将返回:

| id  | project_name        | parent_id | js                                                               |
| --- | ------------------- | --------- | ---------------------------------------------------------------- |
| 1   | Carmichael House    | 0         | {"id": 1, "parent_id": 0, "project_name": "Carmichael House"}    |
| 2   | Carmichael Kitchen  | 1         | {"id": 2, "parent_id": 1, "project_name": "Carmichael Kitchen"}  |
| 3   | Carmichael Bathroom | 1         | {"id": 3, "parent_id": 1, "project_name": "Carmichael Bathroom"} |
| 4   | Dowd Apartment      | 0         | {"id": 4, "parent_id": 0, "project_name": "Dowd Apartment"}      |
| 5   | Dowd Kitchen        | 4         | {"id": 5, "parent_id": 4, "project_name": "Dowd Kitchen"}        |

要生成您的预期输出，我们将自行JOIN该表以查找子记录，并使用

DB Fiddle上的演示

I am expecting this JSON for my jQuery code:

{
  "projects": [
    {
      "id": "1",
      "project_name": "Carmichael House",
      "parent_id": "0",
      "children": [
        {
          "id": "2",
          "project_name": "Carmichael Kitchen",
          "parent_id": "1"
        },
        {
          "id": "3",
          "project_name": "Carmichael Bathroom",
          "parent_id": "1"
        }
      ]
    },
    {
      "id": "2",
      "project_name": "Dowd Apartment",
      "parent_id": "0",
      "children": [
        {
          "id": "4",
          "project_name": "Dowd Kitchen",
          "parent_id": "2"
        }
      ]
    }
  ]
}

This data will come from MySql table tbl_projects:

id
project_name
parent_id

What should the SQL SELECT query be, so that it will output 1 flat table, that can easily be converted into JSON (in PHP or JavaScript/jQuery)?

Am I even approaching this the right way?

解决方案

You can generate JSON content directly from MySQL. Here is a solution that works with MySQL 5.7 or higher.

As a starter, coonsider function JSON_OBJECT(), that generates a JSON object for each record in the table:

SELECT 
    p.*, 
    JSON_OBJECT('id', id, 'project_name', project_name, 'parent_id', parent_id) js
FROM tbl_projects p;

Given your sample data, this returns:

| id  | project_name        | parent_id | js                                                               |
| --- | ------------------- | --------- | ---------------------------------------------------------------- |
| 1   | Carmichael House    | 0         | {"id": 1, "parent_id": 0, "project_name": "Carmichael House"}    |
| 2   | Carmichael Kitchen  | 1         | {"id": 2, "parent_id": 1, "project_name": "Carmichael Kitchen"}  |
| 3   | Carmichael Bathroom | 1         | {"id": 3, "parent_id": 1, "project_name": "Carmichael Bathroom"} |
| 4   | Dowd Apartment      | 0         | {"id": 4, "parent_id": 0, "project_name": "Dowd Apartment"}      |
| 5   | Dowd Kitchen        | 4         | {"id": 5, "parent_id": 4, "project_name": "Dowd Kitchen"}        |

To generate your expected output, we will self-JOIN the table to find children records, and use aggregate function JSON_ARRAYAGG() to generate the inner JSON array. An additional level of aggregation stuffs everything into a single object. As showned in your sample data, I assumed that root projects have parent_id = 0 and that there is only one level of hierarchy:

SELECT JSON_OBJECT('projects', JSON_ARRAYAGG(js)) results
FROM (
    SELECT JSON_OBJECT(
        'id', p.id, 
        'project_name', p.project_name, 
        'parent_id', p.parent_id,
        'children', JSON_ARRAYAGG(
            JSON_OBJECT(
                'id', p1.id, 
                'project_name', p1.project_name, 
                'parent_id', p1.parent_id
            )
        )
    ) js
    FROM tbl_projects p
    LEFT JOIN tbl_projects p1 ON p.id = p1.parent_id
    WHERE p.parent_id = 0
    GROUP BY p.id, p.project_name, p.parent_id
) x

Yields:

| results                                                                                                                                                                                                                                                                                                                                                              |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| {"projects": [{"id": 1, "children": [{"id": 2, "parent_id": 1, "project_name": "Carmichael Kitchen"}, {"id": 3, "parent_id": 1, "project_name": "Carmichael Bathroom"}], "parent_id": 0, "project_name": "Carmichael House"}, {"id": 4, "children": [{"id": 5, "parent_id": 4, "project_name": "Dowd Kitchen"}], "parent_id": 0, "project_name": "Dowd Apartment"}]} |

Demo on DB Fiddle

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