Can You Join Tables Based on Data Stored in JSON Fields in MySQL?

Performing Joins on JSON Fields in MySQL

Question:

In a database with a JSON field storing a list of IDs, is it possible to perform SQL operations on this field and use them to join with another table?

Example:

Consider the following tables:

<code class="sql">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)
);</code>

We want to create a query that returns the following results:

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

Where user_groups stores the list [1, 3], representing group IDs.

Answer:

Yes, it is possible to perform joins on JSON fields in MySQL. Using the JSON_CONTAINS function, we can check if a JSON value contains a specific value:

<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>

In this query, JSON_CONTAINS checks if the user_groups field contains the user_group_id value. If so, it includes the row in the result set. The $ operator in this function denotes that it should search anywhere in the array for the specified value.

This technique allows you to perform joins on JSON fields and extract relevant data from nested structures.

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