MySQL raises ER_JSON_KEY_TOO_BIG (SQLSTATE 22032) when a JSON key exceeds the maximum 255 byte limit.
ER_JSON_KEY_TOO_BIG appears when a MySQL JSON document contains a key longer than 255 bytes. Shorten the key or restructure the JSON object, then re-insert or update the row to resolve the error.
ER_JSON_KEY_TOO_BIG
MySQL returns ER_JSON_KEY_TOO_BIG with SQLSTATE 22032 when it detects a key in a JSON object that exceeds 255 bytes. The server stops the statement and refuses to store or process the document.
This limit was introduced in MySQL 5.7.8 to safeguard performance and indexing. Any INSERT, UPDATE, or JSON function that produces an oversized key triggers the error.
The primary cause is a key name longer than 255 bytes in the JSON text supplied to MySQL. Dynamic key generation, user-supplied data, or concatenation bugs often create such keys.
Another trigger is improper character set handling. Multibyte UTF-8 characters can inflate byte length even when the visible key seems short.
First, identify the offending key. Use JSON_LENGTH or JSON_EXTRACT to isolate long keys. Then shorten or hash the key to 255 bytes or less before writing to the table.
If the key must remain long for application logic, split the data into nested objects with shorter keys or move the data to a relational column.
Bulk imports with auto-generated keys often fail. Pre-validate the JSON in application code or with a staging table.
APIs storing user attributes sometimes let users create long property names. Enforce server-side validation to cap key length.
Validate JSON keys in application logic and deny keys beyond 200 characters to leave room for multibyte growth.
Store large dynamic maps in a separate key-value table instead of an oversized JSON document. Use Galaxy's AI copilot to scan queries for potential key length violations before deployment.
ER_JSON_DOCUMENT_TOO_LARGE occurs when the entire document exceeds 1GB. ER_WRONG_VALUE_FOR_TYPE appears when JSON types mismatch. Both follow similar validation and restructuring approaches.
Code that concatenates user IDs, timestamps, and prefixes can easily create keys over 255 bytes.
Public APIs that accept raw JSON allow clients to post keys of arbitrary length, hitting the limit on insert.
Keys crafted in UTF-8 may look short in characters but exceed 255 bytes when stored.
Fires when a JSON document is larger than 1GB.
Occurs with malformed JSON syntax.
Triggers when a JSON value cannot be cast to the target type.
No. The limit is hard-coded in MySQL. You must refactor keys.
The limit is enforced at the server level, so all engines are affected.
Run a migration script that renames or hashes keys before import.
Galaxy's AI copilot flags long JSON keys during query reviews, preventing failed deployments.
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