MySQL Error 1062

Error number

1062

SQLSTATE

23000

Symbol

ER_DUP_ENTRY

Product

MySQL Server

Versions

MySQL 5.7, 8.0 and 8.4 (8.0 and later name the key as table.key)

Category

Keys & Constraints

Last reviewed

24 October 2026

What it means

Error 1062 means a row would store a value that already exists in a PRIMARY KEY or UNIQUE index, so MySQL rejected the statement.

A PRIMARY KEY or UNIQUE index allows each key value only once. When an INSERT, UPDATE, LOAD DATA or ALTER TABLE would create a second row with a value that is already there, InnoDB stops the statement and MySQL returns 1062. The message gives you the two things you need: the duplicate value ('1') and the key that rejected it (customers.PRIMARY, or the name of a UNIQUE index).

For a key over several columns, the values are joined with a hyphen, so '10-1' means order_id 10 and line_no 1. SQLSTATE 23000 is the standard class for integrity constraint violations; the same class is used for foreign key errors such as 1452, so check the error number, not just the SQLSTATE, in application code.

Common causes

• The same row is inserted twice: a double-clicked submit button, a retried request or a re-run import script.
• The application or an import file supplies key values itself (for example ids copied from another system) and one of them is already taken.
• An UPDATE changes a key column, such as an email address with a UNIQUE index, to a value another row already has.
• ALTER TABLE adds a UNIQUE index or PRIMARY KEY to a column that already holds duplicate values.
• An INSERT ... SELECT or LOAD DATA brings in a source with duplicates, among its own rows or against rows already in the table.

Diagnose it

Read-only These statements only read metadata (information_schema, performance_schema and SHOW statements) or your own data. They do not change data, privileges or configuration, so they are safe to run first.

SELECT index_name, column_name, seq_in_index
FROM information_schema.statistics
WHERE table_schema = DATABASE()
  AND table_name = 'customers'
  AND non_unique = 0
ORDER BY index_name, seq_in_index;

SELECT *
FROM customers
WHERE id = 1;  -- the duplicate value from the message

SELECT name, COUNT(*) AS copies
FROM customers
GROUP BY name
HAVING COUNT(*) > 1
ORDER BY copies DESC;

SHOW CREATE TABLE customers;
SELECT MAX(id) AS highest_id FROM customers;

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

INSERT INTO customers (id, email, name)
VALUES (1, 'sara@example.com', 'Sara')
AS new
ON DUPLICATE KEY UPDATE email = new.email, name = new.name;

INSERT INTO customers (id, email, name)
SELECT s.id, s.email, s.name
FROM staging_customers AS s
WHERE NOT EXISTS (SELECT 1 FROM customers AS c WHERE c.id = s.id);

INSERT INTO customers (email, name) VALUES ('ali@example.com', 'Ali');  -- no id supplied
SELECT LAST_INSERT_ID();

ALTER TABLE customers ADD UNIQUE KEY uq_customers_name (name);

Examples

Inserting a duplicate primary key

CREATE TABLE customers (
    id    INT PRIMARY KEY,
    email VARCHAR(200),
    name  VARCHAR(100)
);

INSERT INTO customers (id, email, name) VALUES (1, 'sara@example.com', 'Sara');
INSERT INTO customers (id, email, name) VALUES (1, 'ali@example.com', 'Ali');  -- id 1 already exists

ERROR 1062 (23000): Duplicate entry '1' for key 'customers.PRIMARY'

An UPDATE that copies a unique email address

CREATE TABLE customers (
    id    INT PRIMARY KEY,
    email VARCHAR(200),
    UNIQUE KEY uq_customers_email (email)
);
INSERT INTO customers VALUES (1, 'sara@example.com'), (2, 'ali@example.com');

UPDATE customers SET email = 'sara@example.com' WHERE id = 2;

ERROR 1062 (23000): Duplicate entry 'sara@example.com' for key 'customers.uq_customers_email'

A duplicate in a multi-column key

CREATE TABLE order_lines (
    order_id INT,
    line_no  INT,
    PRIMARY KEY (order_id, line_no)
);

INSERT INTO order_lines (order_id, line_no) VALUES (10, 1), (10, 1);

ERROR 1062 (23000): Duplicate entry '10-1' for key 'order_lines.PRIMARY'

Adding a UNIQUE index over existing duplicates

CREATE TABLE customers (id INT PRIMARY KEY, name VARCHAR(100));
INSERT INTO customers VALUES (1, 'Sara'), (2, 'Sara');

ALTER TABLE customers ADD UNIQUE KEY uq_name (name);

ERROR 1062 (23000): Duplicate entry 'Sara' for key 'customers.uq_name'

How to prevent it

Let the database generate surrogate keys with AUTO_INCREMENT, and make writes that might run twice idempotent: an upsert for "create or update" actions, or INSERT ... SELECT ... WHERE NOT EXISTS for imports. De-duplicate staging data before loading it, and check for duplicates before adding a UNIQUE index.

Keep the unique index even when the application checks for duplicates, and handle error 1062 (not just SQLSTATE 23000) in your code so a duplicate becomes a clear message such as "this email is already registered" instead of a crash.

Common questions

Learn more on CodeWithSQL

• SQL constraints explained
• Primary key vs foreign key

Official documentation

• MySQL 8.0 server error message reference
• INSERT ... ON DUPLICATE KEY UPDATE statement
• INSERT statement (IGNORE modifier)
• AUTO_INCREMENT handling in InnoDB

Last technically reviewed 24 October 2026; examples and diagnostics run on MySQL 8.0.46. Message templates checked against the server's error catalogue (perror) for that version.