How to Resolve ORA-00001: unique constraint violated

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  • Post category:DBA
  • Post last modified:May 17, 2023

In this blog post, we will explain some common causes and solutions for this error, and how to prevent it from happening in the future. If you are a database developer or administrator, you may have encountered the ORA-00001 error at some point. The ORA-00001 error, commonly known as “unique constraint violated,” occurs when attempting to insert or update data in a table that has a unique constraint or primary key. This means that the data you are trying to insert or update already exists in the table and violates the uniqueness rule. For example, if you have a table of customers with a unique constraint on the email column, you cannot insert two customers with the same email address.

Causes of ORA-00001

There are several possible scenarios that can lead to the ORA-00001 error. Here are some examples:

  • Duplicate primary key:

CREATE TABLE employees (
employee_name VARCHAR2(50)
INSERT INTO employees (employee_id, employee_name) VALUES (1001, ‘John Doe’);
INSERT INTO employees (employee_id, employee_name) VALUES (1001, ‘Jane Smith’); — Duplicate primary key

  • Duplicate unique index:

CREATE TABLE customers (
customer_id NUMBER,
customer_name VARCHAR2(50)
CREATE UNIQUE INDEX idx_customers_id ON customers (customer_id);
INSERT INTO customers (customer_id, customer_name) VALUES (2001, ‘John Doe’);
INSERT INTO customers (customer_id, customer_name) VALUES (2001, ‘Jane Smith’); — Duplicate unique index

  • Sequence gaps or overlaps:

INSERT INTO customers (customer_id, customer_name) VALUES (seq_customers.NEXTVAL, ‘John Doe’);
INSERT INTO customers (customer_id, customer_name) VALUES (1001, ‘Jane Smith’); — Attempt to insert a value already generated by the sequence

  • Data Import with duplicate Values

— Existing data in the table INSERT INTO customers (customer_id, customer_name) VALUES (4001, ‘John Doe’);– During data import
INSERT INTO customers (customer_id, customer_name) VALUES (4001, ‘Jane Smith’); — Duplicate value during data import

Solutions for ORA-00001

Depending on the cause and context of the ORA-00001 error, there are different ways to resolve it. here are some possible solutions along with examples:

  • Identify the duplicate values:

Analyze the data causing the violation and identify the duplicate values that are conflicting with the unique constraint.

SELECT column1, column2 FROM table_name WHERE column1 = ‘duplicate_value’;

  • Delete or update the duplicate values:

Remove or modify the duplicate values to ensure uniqueness.

DELETE FROM table_name
WHERE column1 = ‘duplicate_value’;

  • Use MERGE statement:

Use the MERGE statement to merge duplicate records or update existing records.


MERGE INTO table_name dst
USING (SELECT ‘duplicate_value’ AS column1, ‘new_value’ AS column2 FROM dual) src
ON (dst.column1 = src.column1)
WHEN MATCHED THEN UPDATE SET dst.column2 = src.column2
WHEN NOT MATCHED THEN INSERT (column1, column2) VALUES (src.column1, src.column2);

  • Review unique constraint definition:

Verify that the unique constraint is correctly defined and aligns with the desired uniqueness criteria.


ALTER TABLE table_name
ADD CONSTRAINT constraint_name UNIQUE (column1, column2);

  • Check concurrent transactions:

Examine concurrent transactions to ensure they are not causing conflicts by trying to insert duplicate values.


— Coordinate transactions to avoid conflicts
Transaction 1:
INSERT INTO table_name (column1, column2) VALUES (‘duplicate_value’, ‘new_value’);

Transaction 2:
— Check if the value already exists before inserting
IF NOT EXISTS (SELECT 1 FROM table_name WHERE column1 = ‘duplicate_value’) THEN
INSERT INTO table_name (column1, column2) VALUES (‘duplicate_value’, ‘new_value’);

Preventing ORA-00001

You can take the following measures to prevent ORA-00001 errors, which indicate unique constraint violations:

  • Use proper validation before insertion

Before inserting data into a table, it is important to perform validation checks to ensure that the values being inserted do not violate any unique constraints.


// Check if the value already exists before inserting
if (!isValueExists(value)) {
// Perform insert operation

  • Implement error handling and retry mechanisms:

To handle the ORA-00001 error smoothly, you can implement retry mechanisms in your code that allow for retrying the operation if a unique constraint violation occurs.


int maxRetries = 3;
int retryCount = 0;
boolean operationSuccessful = false; while (!operationSuccessful && retryCount < maxRetries) {
try {
// Perform insert operation
operationSuccessful = true;
} catch (SQLException e) {
if (isUniqueConstraintViolation(e)) {
// Handle the error and retry the operation
} else {
// Handle other types of errors

  • Implement proper transaction management:

Utilize transactions to ensure atomicity and consistency in your database operations, reducing the chances of unique constraint violations.


try {
// Begin transaction
// Perform insert/update/delete operations
// Commit the transaction
} catch (SQLException e) {
// Handle the exception and perform rollback if necessary

  • Use constraints and indexes effectively:

Define appropriate unique constraints and indexes on the relevant columns to enforce uniqueness and improve query performance.


ALTER TABLE table_name
ADD CONSTRAINT constraint_name UNIQUE (column1, column2);

  • Implement data validation at the application level:

Apply strict data validation checks at the application level to ensure that duplicate values are not inserted.


// Validate the value before attempting to insert
if (isValueValid(value)) {
// Perform insert operation

By incorporating these preventive measures into your application’s design and development process, you can minimize the occurrence of ORA-00001 errors and maintain the integrity of your database’s unique constraints.

Read Related Topics

ORA-0000: normal, successful completion

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