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Description

This error indicates that you are attempting to create a foreign key constraint with a name that already exists within the same database scope or table. It typically occurs during schema modifications or database migrations when defining new tables or altering existing ones, preventing the DDL statement from completing successfully.

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Error Message

Duplicate foreign key constraint name '%s'

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Known Causes

3 known causes

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Non-Unique Constraint Name

You attempted to create a foreign key constraint using a name that is already assigned to another foreign key within the same database or table.

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Repeated Script Execution

This error frequently occurs when a database schema creation or alteration script is executed multiple times, attempting to define the same foreign key constraint more than once.

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Schema Migration Conflict

During database migrations, a conflict can arise if the migration process attempts to add a foreign key with a name that already exists in the target schema.

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Solutions

3 solutions available

1. Rename the Duplicate Foreign Key Constraint easy

Identify and rename the conflicting foreign key constraint name.

1

Identify the table and the offending foreign key name. The error message '%s' will typically contain the name. You can find which tables have foreign keys by querying the `INFORMATION_SCHEMA.KEY_COLUMN_USAGE` table.

SELECT TABLE_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE REFERENTIAL_CONSTRAINTS.CONSTRAINT_SCHEMA = DATABASE() AND CONSTRAINT_TYPE = 'FOREIGN KEY' AND CONSTRAINT_NAME = 'your_duplicate_fk_name';

2

Once identified, use the `ALTER TABLE` statement to rename one of the duplicate foreign key constraints.

ALTER TABLE your_table_name RENAME CONSTRAINT your_duplicate_fk_name TO a_new_unique_fk_name;

3

If you are creating the table with the duplicate constraint, modify the `CREATE TABLE` statement to use a unique name for the foreign key.

CREATE TABLE your_table_name (
    id INT PRIMARY KEY,
    related_id INT,
    -- other columns
    CONSTRAINT your_new_unique_fk_name FOREIGN KEY (related_id) REFERENCES another_table(id)
);

2. Drop and Recreate the Foreign Key Constraint easy

Remove the existing foreign key and add it back with a unique name.

1

Identify the table and the foreign key constraint name that is causing the duplication.

SHOW CREATE TABLE your_table_name;

2

Drop the existing foreign key constraint. Replace `your_fk_name` with the actual name of the constraint.

ALTER TABLE your_table_name DROP FOREIGN KEY your_fk_name;

3

Recreate the foreign key constraint with a unique name. Ensure `your_new_unique_fk_name` is distinct from any other foreign key names in your schema.

ALTER TABLE your_table_name ADD CONSTRAINT your_new_unique_fk_name FOREIGN KEY (your_column) REFERENCES referenced_table(referenced_column);

3. Review and Consolidate Schema Definitions medium

Thoroughly inspect your schema creation scripts or migration files to ensure no duplicate foreign key names are being defined.

1

Examine all `CREATE TABLE` statements and `ALTER TABLE ADD CONSTRAINT` statements in your database schema definition files (e.g., SQL scripts, migration files).

Open your schema definition files in a text editor or IDE.

2

Search for all instances where foreign key constraints are defined. Pay close attention to the `CONSTRAINT` keyword and the name assigned to the foreign key.

Look for patterns like: `CONSTRAINT constraint_name FOREIGN KEY (...) REFERENCES ...`

3

Identify any duplicate `constraint_name` values across different tables or within the same table definition.

Manually compare the names or use command-line tools for searching and pattern matching.

4

Modify the schema definition files to assign unique names to all foreign key constraints before applying them to the database.

Example: Change `CONSTRAINT fk_users_orders` to `CONSTRAINT fk_users_orders_table1` if a conflict is found.

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Related Errors

5 related errors

MariaDB Error 1826: Duplicate Foreign Key Name