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Description

This error occurs when you attempt to use the `TRUNCATE TABLE` statement on a parent table that is referenced by one or more foreign key constraints in other tables. MySQL prevents this operation to maintain referential integrity, as truncating would orphan child records.

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Error Message

Cannot truncate a table referenced in a foreign key constraint (%s)

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Known Causes

3 known causes

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Truncating a Parent Table

You tried to truncate a table that acts as the 'parent' in a foreign key relationship, meaning other tables depend on its records.

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Unaware of Foreign Key Dependencies

The `TRUNCATE TABLE` command was executed without realizing that the target table is part of an active foreign key constraint.

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Incorrect Database Design

The database schema might have foreign key constraints that are not intended for the desired data manipulation workflow, leading to unexpected errors.

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Solutions

3 solutions available

1. Temporarily Disable Foreign Key Checks easy

Quickly truncate by disabling constraint checks for the current session.

1

Start a new MySQL session or ensure you are in one where you want to perform the truncate operation.

2

Disable foreign key checks for the current session.

SET FOREIGN_KEY_CHECKS = 0;

3

Execute the TRUNCATE TABLE statement on the referenced table.

TRUNCATE TABLE your_table_to_truncate;

4

Re-enable foreign key checks to restore constraint integrity.

SET FOREIGN_KEY_CHECKS = 1;

2. Drop and Recreate Foreign Key Constraints medium

Permanently remove and then re-add constraints for a cleaner truncation.

1

Identify the foreign key constraint(s) referencing the table you want to truncate. You can find this information using `SHOW CREATE TABLE` on the referencing table.

SHOW CREATE TABLE referencing_table_name;

2

Once identified, drop the foreign key constraint(s) from the referencing table(s). Replace `fk_constraint_name` with the actual name of the constraint.

ALTER TABLE referencing_table_name DROP FOREIGN KEY fk_constraint_name;

3

Execute the TRUNCATE TABLE statement on the table that was being referenced.

TRUNCATE TABLE your_table_to_truncate;

4

Recreate the foreign key constraint(s) on the referencing table(s). You will need the original definition, which you can get from the `SHOW CREATE TABLE` output in step 1. Ensure the `ON UPDATE` and `ON DELETE` clauses are correctly set.

ALTER TABLE referencing_table_name ADD CONSTRAINT fk_constraint_name FOREIGN KEY (referencing_column) REFERENCES your_table_to_truncate (referenced_column) ON DELETE NO ACTION ON UPDATE NO ACTION;

3. Delete Rows from the Referenced Table medium

Remove data from the referencing table before truncating the parent table.

1

Identify the foreign key relationship. Determine which table(s) have foreign keys pointing to the table you intend to truncate.

2

Delete all rows from the referencing table(s) that would violate the foreign key constraint if the parent table were truncated. This effectively removes the references.

DELETE FROM referencing_table_name WHERE referencing_column IN (SELECT referenced_column FROM your_table_to_truncate);

3

Once all referencing rows are removed, you can safely truncate the parent table.

TRUNCATE TABLE your_table_to_truncate;

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Related Errors

5 related errors

MySQL Error 1701: Truncate Foreign Key Table