ER_DUP_UNIQUE is raised when an INSERT or UPDATE duplicates a value protected by a UNIQUE or PRIMARY KEY index.
MySQL Error 1169 (ER_DUP_UNIQUE) appears when an INSERT or UPDATE tries to write a duplicate value into a column backed by a UNIQUE or PRIMARY KEY index. Remove or change the duplicate value, or adjust the index, to resolve the problem.
Can't write, because of unique constraint, to table '%s'
MySQL raises error 1169 with condition ER_DUP_UNIQUE when a write operation would create duplicate values in a column or set of columns that have a UNIQUE or PRIMARY KEY constraint.
The server stops the statement, returns SQLSTATE 23000, and protects data integrity. Understanding why the duplicate occurs lets you apply the correct fix quickly.
The error happens during INSERT, REPLACE, LOAD DATA, or UPDATE statements that target a table with unique indexes.
If the new key already exists in the index, MySQL blocks the write and throws ER_DUP_UNIQUE.
It can also surface in replication when downstream servers reapply statements that introduce duplicates not present on the primary.
Ignoring the error leaves data unchanged and can break application logic that assumes the write succeeded. Continuous failures can clog job queues and replication, slowing downstream analytics tools like Galaxy.
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You can set SQL_MODE=IGNORE_SPACE or use INSERT IGNORE, but disabling constraints is risky and not recommended for production.
Use INSERT ... ON DUPLICATE KEY UPDATE or the REPLACE statement to have MySQL update or replace the existing row.
If you insert explicit ids during restore, the AUTO_INCREMENT counter may lag behind, so the next automatic id overlaps. Reset AUTO_INCREMENT to max(id)+1.
Galaxy's AI copilot checks existing keys during query writing and warns about potential duplicates, reducing runtime failures.
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