<p>MySQL raises this error when an index COMMENT exceeds the allowed length (1024 characters).</p>
<p>MySQL Error 1688 ER_TOO_LONG_INDEX_COMMENT triggers when the COMMENT attached to an index is longer than the permitted 1024 characters. Shorten or remove the comment, then recreate or alter the index to resolve the issue.</p>
Comment for index '%s' is too long (max = %lu)
MySQL throws error 1688 ER_TOO_LONG_INDEX_COMMENT when you create or alter an index whose COMMENT string surpasses the limit defined by max_index_comment_length (1024 characters in modern releases).
The database aborts the statement, leaving the existing schema intact. Index comments are stored in data dictionary tables, so the limit keeps metadata compact and engine compatible.
Oversized COMMENT clauses in CREATE TABLE, CREATE INDEX, or ALTER TABLE commands directly cause the error. It can also appear during logical dumps or ORM migrations that generate long auto comments.
Reduce the comment length below 1024 characters or omit it entirely, then rerun the DDL. When comments are auto generated, adjust the template or configuration that produces them.
Database migrations from MariaDB may contain 2048-character comments. Search and truncate those lines before import.
Framework-driven comments that embed JSON can exceed limits. Switch to external documentation or hash references instead.
Keep index comments concise and focused on purpose, not business logic. Store verbose notes in version control or a data catalog like Galaxy Collections.
Implement CI checks that scan generated DDL for comment length violations before deployment.
ER_TOO_LONG_TABLE_COMMENT occurs when table comments are too long. Shorten the TABLE COMMENT clause to resolve.
Developers sometimes paste full specifications or ticket links, pushing the comment past 1024 characters.
Some ORMs serialize column definitions into the comment, easily breaching the limit.
Imports from MariaDB or older MySQL forks may include longer comments not accepted by current MySQL versions.
Tools that embed Markdown or JSON into comments often exceed the supported length.
Triggered when a TABLE COMMENT exceeds 2048 characters. Fix by shortening the comment.
Occurs if a COLUMN COMMENT is longer than 1024 characters. Trim the comment and reapply schema changes.
Appears when combined indexed column length exceeds maximum. Reduce indexed prefix length or column size.
No. The limit is hard coded in MySQL source and cannot be adjusted via configuration.
No data is touched. Only the DDL statement fails, leaving tables and indexes unchanged.
Galaxy's SQL editor surfaces schema validation warnings and can lint comment lengths before you run DDL, preventing the error in development.
All maintained MySQL versions, including 5.7 and 8.x, enforce the 1024-character limit.
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