📋

Description

This error occurs when you attempt to create a direct index on a JSON data type column in MySQL. MySQL mandates that indexes on JSON columns must be created indirectly, by first defining a generated column that extracts a specific path from the JSON document.

💬

Error Message

JSON column '%s' supports indexing only via generated columns on a specified JSON path.

🔍

Known Causes

3 known causes

⚠️

Direct Index on JSON Column

Attempting to create a standard index (e.g., B-tree) directly on a JSON data type column, which MySQL does not support.

⚠️

Missing Generated Column

Trying to index a specific value within a JSON document without first defining a generated column to extract that scalar value.

⚠️

Incorrect Indexing Syntax

Using `CREATE INDEX` syntax that is valid for scalar data types but not for the unique requirements of JSON columns in MySQL.

🛠️

Solutions

3 solutions available

1. Create a Generated Column for Indexing medium

Extract the desired JSON path into a generated column and index that column.

1

Identify the JSON column and the specific JSON path you want to index. For example, if your JSON column is named `data` and you want to index the value at `$.user.id`, you would use the path `$.user.id`.

2

Add a new generated column to your table that extracts the value from the JSON path. The `STORED` keyword ensures the value is physically stored, making it indexable. Replace `your_table`, `generated_column_name`, `json_column_name`, and `json_path` with your actual table, desired column name, JSON column name, and JSON path respectively.

ALTER TABLE your_table ADD COLUMN generated_column_name data_type
GENERATED ALWAYS AS (JSON_UNQUOTE(JSON_EXTRACT(json_column_name, '$.your.json.path'))) STORED;

3

Create an index on the newly created generated column.

CREATE INDEX idx_generated_column ON your_table (generated_column_name);

4

Update your queries to use the `generated_column_name` instead of directly querying the JSON column for filtering or sorting operations that require indexing.

2. Use Virtual Generated Columns (for smaller datasets or less frequent indexing) medium

Create a virtual generated column for indexing, which is computed on the fly.

1

Identify the JSON column and the specific JSON path you want to index. For example, if your JSON column is named `data` and you want to index the value at `$.user.id`, you would use the path `$.user.id`.

2

Add a new virtual generated column to your table. Virtual columns are not stored physically, saving disk space but potentially incurring a slight performance overhead during reads. Replace `your_table`, `generated_column_name`, `json_column_name`, and `json_path` with your actual table, desired column name, JSON column name, and JSON path respectively. Ensure the `data_type` is appropriate for the extracted JSON value.

ALTER TABLE your_table ADD COLUMN generated_column_name data_type
GENERATED ALWAYS AS (JSON_UNQUOTE(JSON_EXTRACT(json_column_name, '$.your.json.path'))) VIRTUAL;

3

Create an index on the newly created virtual generated column.

CREATE INDEX idx_generated_column ON your_table (generated_column_name);

4

Update your queries to use the `generated_column_name` for indexed operations.

3. Re-evaluate Indexing Strategy for JSON Data advanced

Consider if indexing is truly necessary for the specific JSON path or if alternative data structures are more appropriate.

1

Analyze the queries that are attempting to index the JSON column. Understand the frequency and criticality of these queries.

2

Determine if the data within the JSON path is frequently used for filtering, sorting, or joining. If not, direct indexing might be an unnecessary optimization.

3

Consider if the JSON structure can be flattened into separate, traditional columns. If a specific JSON key-value pair is always present and critical for querying, it might be more efficient to have it as a dedicated column with a standard index.

4

If the JSON data is highly variable and complex, and direct indexing on specific paths is not performant, consider alternative approaches like full-text search indexing for text-based JSON content, or denormalizing critical data into separate tables.

🔗

Related Errors

5 related errors

MySQL Error 3152: Invalid JSON Column Indexing