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Description

This error indicates that you are attempting to create or modify a table with a `CHECK` constraint that has a name already in use. MySQL requires all `CHECK` constraint names within a table to be unique to prevent naming collisions and ensure proper constraint management.

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Error Message

Duplicate check constraint name '%s'.

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Known Causes

4 known causes

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Accidental Constraint Name Reuse

A new `CHECK` constraint was defined using a name that was previously used for another `CHECK` constraint on the same table.

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Copy-Pasting SQL with Existing Names

SQL scripts containing `CREATE TABLE` or `ALTER TABLE` statements were copied and executed without updating constraint names, leading to a conflict.

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Renaming Collision During Alteration

An `ALTER TABLE` operation attempted to rename an existing `CHECK` constraint to a name that is already in use by another constraint.

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Schema Migration Issues

During a database schema migration or deployment, a script tried to apply a `CHECK` constraint definition with a name that already exists in the target database.

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Solutions

3 solutions available

1. Rename the Conflicting Check Constraint easy

Modify the SQL statement to use a unique name for the check constraint.

1

Identify the SQL statement that is attempting to create a check constraint with a name that already exists. This usually occurs during `ALTER TABLE` or `CREATE TABLE` statements.

2

Locate the `CONSTRAINT` clause within your SQL statement. You will see a name assigned to the check constraint, like `CONSTRAINT constraint_name CHECK (...)`.

CONSTRAINT `existing_constraint_name` CHECK (`column_name` > 0)

3

Change the `existing_constraint_name` to a new, unique name. Ensure this new name does not already exist in the database for any other constraints (primary keys, foreign keys, unique constraints, or other check constraints).

CONSTRAINT `new_unique_constraint_name` CHECK (`column_name` > 0)

4

Execute the modified SQL statement.

2. Drop the Existing Check Constraint medium

Remove the pre-existing check constraint if it's no longer needed or is redundant.

1

Connect to your MySQL database using a client like `mysql` command-line tool or MySQL Workbench.

2

Query the `information_schema.TABLE_CONSTRAINTS` table to find the name of the existing constraint that is causing the conflict. You can filter by `CONSTRAINT_TYPE = 'CHECK'` and the table name.

SELECT CONSTRAINT_NAME FROM information_schema.TABLE_CONSTRAINTS WHERE CONSTRAINT_TYPE = 'CHECK' AND TABLE_SCHEMA = 'your_database_name' AND TABLE_NAME = 'your_table_name';

3

Once you have identified the name of the duplicate constraint (let's call it `duplicate_constraint_name`), use the `ALTER TABLE ... DROP CONSTRAINT` statement to remove it. Note that MySQL versions before 8.0.16 did not support `DROP CONSTRAINT` directly for check constraints; you would use `ALTER TABLE ... DROP CHECK constraint_name`.

-- For MySQL 8.0.16 and later:
ALTER TABLE `your_table_name` DROP CONSTRAINT `duplicate_constraint_name`;

-- For older MySQL versions:
ALTER TABLE `your_table_name` DROP CHECK `duplicate_constraint_name`;

4

After dropping the existing constraint, you can now execute your original `ALTER TABLE` or `CREATE TABLE` statement with the new check constraint (which should have a unique name).

3. Review and Consolidate Check Constraints advanced

Examine all check constraints on a table to ensure no naming collisions and to simplify if possible.

1

List all existing constraints for a specific table to understand the current schema.

SHOW CREATE TABLE `your_table_name`;

2

Analyze the output of `SHOW CREATE TABLE`. Identify all `CONSTRAINT` definitions, paying close attention to those with the `CHECK` keyword. Note their names and the conditions they enforce.

3

If you find multiple check constraints that could be combined into a single, more comprehensive constraint, consider dropping the redundant ones and creating a new, consolidated constraint with a unique name. This can sometimes simplify management and avoid naming conflicts.

-- Example: Dropping two constraints and adding one
ALTER TABLE `your_table_name` DROP CHECK `constraint1`;
ALTER TABLE `your_table_name` DROP CHECK `constraint2`;
ALTER TABLE `your_table_name` ADD CONSTRAINT `new_consolidated_check` CHECK (`column1` > 0 AND `column2` IS NOT NULL);

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If the conflict arises from constraints defined in different migration scripts or application versions, ensure your deployment process handles constraint naming consistently or includes logic to drop existing constraints before attempting to create new ones with the same intended purpose but different names.

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Related Errors

5 related errors

MySQL Error 3822: Duplicate Check Constraint Name