EC
1022
MariaDBERRORNotableConstraintHIGH confidence

Can't write — duplicate key in table

Production Risk

Medium — write is rejected; application must handle the error.

What this means

ER_DUP_KEY (1022, SQLSTATE 23000) is raised when an INSERT or UPDATE violates a unique key constraint. It is a generic form; error 1062 (ER_DUP_ENTRY) provides a more specific message including the duplicate value.

Why it happens
  1. 1Inserting a row whose key value already exists in the table
  2. 2Updating a row to a key value that conflicts with an existing row
  3. 3Bulk load data with duplicate values in a unique column
How to reproduce
trigger — this will error
trigger — this will error
INSERT INTO t (id) VALUES (1);
INSERT INTO t (id) VALUES (1); -- duplicate

expected output

ERROR 1022 (23000): Can't write; duplicate key in table 't'

Fix

Use INSERT IGNORE or ON DUPLICATE KEY UPDATE

WHEN Duplicates are expected and should be silently skipped or merged.

Use INSERT IGNORE or ON DUPLICATE KEY UPDATE
INSERT IGNORE INTO t (id) VALUES (1);
-- or:
INSERT INTO t (id, val) VALUES (1, 'new')
ON DUPLICATE KEY UPDATE val = VALUES(val);

Why this works

INSERT IGNORE discards the duplicate row silently; ON DUPLICATE KEY UPDATE merges the new values into the existing row.

What not to do

✕ Suppress 1022 without investigating duplicate sources

Silently ignoring duplicates may hide data integrity bugs in the application layer.

Sources
Official documentation ↗

MySQL 8.0 — 1022 ER_DUP_KEY

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