How can you join MySQL tables based on data within a JSON field?

Using MySQL JSON Field for Complex Table Joins

Problem:

In a MySQL database schema, a JSON field stores a list of IDs. The goal is to perform operations on this JSON field and use the results in an SQL query to join the user table with a user group table.

Example Scenario:

Consider the following tables:

CREATE TABLE user (
    user_id INT,
    user_name VARCHAR(50),
    user_groups JSON
);

CREATE TABLE user_group (
    user_group_id INT,
    group_name VARCHAR(50)
);

With the following data:

INSERT INTO user_group (user_group_id, group_name) VALUES (1, 'Group A');
INSERT INTO user_group (user_group_id, group_name) VALUES (2, 'Group B');
INSERT INTO user_group (user_group_id, group_name) VALUES (3, 'Group C');

INSERT INTO user (user_id, user_name, user_groups) VALUES (101, 'John', '[1,3]');

Desired Result:

The desired result is a query that retrieves the following data:

user_id | user_name | user_group_id | group_name|
-------------------------------------------------
101     | John      | 1             | Group A
101     | John      | 3             | Group C

Solution:

The solution involves using the JSON_CONTAINS function to check if the user group ID exists within the JSON field of the user table.

<code class="sql">SELECT 
       u.user_id, 
       u.user_name, 
       g.user_group_id,
       g.group_name
   FROM user u
   LEFT JOIN user_group g on JSON_CONTAINS(u.user_groups, CAST(g.user_group_id as JSON), '$')</code>

Note:

The $ operator in the JSON_CONTAINS function represents the root of the JSON document.

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