<p>The server refuses to drop or rename the FTS_DOC_ID column during an ALTER TABLE because it is essential for a full-text index, triggering error 1856.</p>
<p>MySQL Error 1856: ER_ALTER_OPERATION_NOT_SUPPORTED_REASON_CHANGE_FTS means the ALTER TABLE statement tried to drop or rename the mandatory FTS_DOC_ID column that underpins a full-text index. Keep the column or rebuild the index to resolve the issue.</p>
Cannot drop or rename FTS_DOC_ID
Error 1856 fires when an ALTER TABLE attempts to drop or rename the hidden FTS_DOC_ID column that MySQL automatically creates to support full-text indexes in InnoDB tables.
The engine blocks that change because FTS_DOC_ID holds internal document identifiers needed for indexing and query processing. Removing or renaming it would corrupt the full-text index.
The message shows up during schema migrations, automated refactors, or manual ALTER TABLE statements that explicitly reference FTS_DOC_ID or rename the table while using CHANGE COLUMN incorrectly.
It can also surface in tools that generate change scripts without filtering out system columns introduced by MySQL.
Leaving an unsuccessful migration in place blocks deployment pipelines and can leave your database in an inconsistent state. Addressing the root cause ensures reliable releases and preserves search performance.
Resolving the issue also avoids downtime in production environments where full-text search is mission-critical.
Developers sometimes try to clean up columns they do not recognize, accidentally targeting FTS_DOC_ID.
Migration generators may treat all columns equally and try to rename FTS_DOC_ID with the rest of the schema.
Altering an InnoDB table with full-text indexes to another engine triggers a hidden attempt to drop FTS_DOC_ID.
Creating a new table without full-text support and swapping names can indirectly drop the column.
Raised when attempting to explicitly drop FTS_DOC_ID without touching a full-text index.
Occurs during ALTER TABLE when a column comment exceeds the 1024-byte limit.
Appears if an ALTER TABLE adds a column that duplicates an existing name.
No. MySQL automatically creates and maintains the column when you add a full-text index to an InnoDB table.
The column is hidden from standard queries. You will only see it in SHOW CREATE TABLE output.
Yes. Once the last full-text index is removed, MySQL drops FTS_DOC_ID automatically.
Galaxy highlights hidden columns, warns during schema changes, and offers AI suggestions to adjust migrations safely.
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