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Description

This error occurs when a functional index attempts to process a value using a `CAST` operation, but the value is not valid JSON. It typically signifies a mismatch between the expected JSON format within the index expression and the actual data being processed, leading to a casting failure.

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Error Message

Invalid JSON value for CAST for functional index '%s'.

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Known Causes

3 known causes

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Malformed JSON Data

The JSON data stored in the column referenced by the functional index is syntactically incorrect, incomplete, or not valid JSON, leading to a `CAST` failure.

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Incorrect Data Type Casting

The functional index expression attempts to `CAST` a non-JSON string or value into a JSON data type, but the source data cannot be interpreted as valid JSON.

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Mismatched Index Expression Logic

The logic within the functional index expression expects a JSON value for a `CAST` operation, but the actual result of the expression yields a non-JSON value.

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Solutions

3 solutions available

1. Correct JSON Structure in Data easy

Ensure all JSON data being inserted or updated conforms to valid JSON syntax.

1

Review the data being inserted or updated into the table that has the functional index. Identify any JSON values that might be malformed.

2

Use a JSON validator tool or online validator to check the syntax of your JSON data. Common issues include missing commas, incorrect quote usage, or trailing commas.

Example of invalid JSON: {"key": "value" "another_key": "another_value"}
Example of valid JSON: {"key": "value", "another_key": "another_value"}

3

Correct the malformed JSON in your data source or in the `INSERT` or `UPDATE` statements. Re-attempt the operation.

2. Adjust Functional Index Definition medium

Modify the functional index to use a JSON function that handles potential invalid values gracefully.

1

Identify the functional index causing the error. This is usually indicated by the '%s' placeholder in the error message.

2

Examine the `CREATE INDEX` statement for the functional index. The error occurs during the `CAST` operation, implying the data might not be directly castable or the path might be incorrect.

Example of potentially problematic index:
CREATE INDEX idx_json_value ON my_table (CAST(json_column->'$.some_key' AS UNSIGNED));

3

Consider using `JSON_UNQUOTE` if the index is on a string value and quotes are causing issues, or adjust the JSON path to be more robust. If the data might be missing the key or is not the expected type, consider using `JSON_EXTRACT` with a default value or a more forgiving cast.

Example using JSON_UNQUOTE:
CREATE INDEX idx_json_unquoted_value ON my_table (JSON_UNQUOTE(json_column->'$.some_key'));

Example using JSON_EXTRACT with a default for potential missing keys:
CREATE INDEX idx_json_safe_extract ON my_table (CAST(JSON_EXTRACT(json_column, '$.some_key', 0) AS UNSIGNED));

4

Drop the existing index and recreate it with the adjusted definition.

DROP INDEX idx_json_value ON my_table;
-- Recreate with corrected definition

3. Validate JSON Data Type Before Indexing advanced

Implement checks in your application or triggers to ensure JSON data is valid before it reaches the database.

1

In your application code (e.g., Python, Java, PHP), before sending data to MySQL, use a JSON parsing library to validate the structure and content of your JSON objects.

Python example:
import json

try:
    data = json.loads(json_string)
    # Further validation of data content if needed
except json.JSONDecodeError as e:
    print(f"Invalid JSON: {e}")
    # Handle the error, e.g., log it, return an error to the user

2

Alternatively, create database triggers that execute `JSON_VALID()` on `INSERT` and `UPDATE` operations for the relevant table. This adds overhead but ensures data integrity at the database level.

CREATE TRIGGER before_insert_validate_json
BEFORE INSERT ON my_table
FOR EACH ROW
BEGIN
    IF NOT JSON_VALID(NEW.json_column) THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid JSON format in json_column';
    END IF;
END;

CREATE TRIGGER before_update_validate_json
BEFORE UPDATE ON my_table
FOR EACH ROW
BEGIN
    IF NOT JSON_VALID(NEW.json_column) THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid JSON format in json_column';
    END IF;
END;

3

If validation fails (either in application or via trigger), prevent the operation and provide informative feedback to the user or log the error for investigation.

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Related Errors

5 related errors

MySQL Error 3903: Invalid JSON for Functional Index