<p>The error appears when an ALTER TABLE statement resequences an AUTO_INCREMENT column and generates duplicate values that clash on a case-insensitive primary or unique key.</p>
<p>MySQL Error 1569: ER_DUP_ENTRY_AUTOINCREMENT_CASE arises when ALTER TABLE resets an AUTO_INCREMENT column and creates a duplicate key on a case-insensitive index. Preserve or reseed existing values, or drop the conflicting index before altering the column to resolve the issue.</p>
ALTER TABLE causes auto_increment resequencing, resulting
The server throws Error 1569 with message ER_DUP_ENTRY_AUTOINCREMENT_CASE when an ALTER TABLE operation forces MySQL to resequence an AUTO_INCREMENT column and the new sequence collides with existing values on a case-insensitive primary or unique key.
This error is important because MySQL cancels the statement to protect data integrity, leaving schema changes incomplete and potentially blocking deployment scripts.
The error usually appears during column type changes, engine conversions, or index modifications that require rebuilding the table. In that process MySQL may renumber the AUTO_INCREMENT column, producing duplicate numeric values that differ only in letter case on accompanying varchar columns within the same composite key.
Unresolved, the schema change never completes, continuous integration jobs fail, and application releases remain blocked. Ignoring the error can also hide data quality issues that surface later as silent duplicates or orphaned rows.
MySQL rebuilds the table and recalculates AUTO_INCREMENT values, but case-insensitive indexes treat 'A1' and 'a1' as identical, so the new numeric key collides with an existing row.
Preserve current AUTO_INCREMENT values, reseed the counter above the highest existing value, or temporarily drop the conflicting unique index before altering the table and recreate it afterwards.
An ALTER TABLE that converts InnoDB to MyISAM can trigger resequencing; set AUTO_INCREMENT explicitly after the conversion. Migrating from varchar primary key to composite numeric key also risks collision; update all records first to ensure uniqueness.
Run SELECT MAX(id) to capture the top numeric value before altering tables. Use explicit ALTER TABLE ... AUTO_INCREMENT = n to seed the next value. Maintain consistent case in key columns and prefer case-sensitive collations where possible.
Error 1062 Duplicate entry occurs when inserting a key that already exists. Error 1169 Can't write, duplicate key in table arises during bulk inserts. These differ by operation but share similar fixes around unique key management.
Engine or charset conversions rebuild the table and recalculate sequence numbers, causing duplicates.
Composite keys containing varchar columns in case-insensitive collations treat A and a as the same, so numeric resequencing collides.
Setting AUTO_INCREMENT to a lower value than existing records forces MySQL to generate duplicates.
Bulk loads that bypass constraints can insert duplicates that only surface when an index is rebuilt.
Occurs during INSERT or UPDATE when a unique or primary key collision happens.
Triggered on bulk inserts or LOAD DATA when duplicates exist.
Appears when referenced key contains duplicate or null values.
Signifies naming conflicts when creating triggers, similar duplicate condition on object names.
Error 1569 is present from MySQL 5.6 onward, including 8.0, because the underlying table rebuild logic is unchanged.
You can set collation_connection to a binary collation for the session, but permanent fixes involve adjusting the column collation or data.
No. The resequencing only happens when ALTER TABLE rebuilds or resets the column, not during ordinary INSERT operations.
Galaxy highlights potential duplicate key risks in real time and lets you preview ALTER statements. You can run SELECT MAX(id) snippets instantly and share safe migration scripts with your team.
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