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Description

MySQL Error 1825 indicates that the foreign key constraint definition contains options or attributes that are not valid or supported. This typically occurs when creating or altering a table with a foreign key that specifies unsupported `ON DELETE`/`ON UPDATE` actions, `MATCH` clauses, or has incompatible column definitions.

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Error Message

Failed to add the foreign key constraint on table '%s'. Incorrect options in FOREIGN KEY constraint '%s'

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Known Causes

4 known causes

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Invalid ON DELETE/ON UPDATE Action

Specifying an unsupported action like `SET DEFAULT` for `ON DELETE` or `ON UPDATE` clauses in the foreign key definition.

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Unsupported MATCH Clause

Attempting to use `MATCH FULL` or `MATCH PARTIAL` in the foreign key definition, which are not supported by MySQL.

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Column Definition Incompatibility

The character set, collation, or data type attributes of the foreign key column do not precisely match those of the referenced parent column.

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Syntax Error in Constraint Options

A general syntax error or typo in the foreign key constraint definition leads to unrecognized or invalid options.

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Solutions

4 solutions available

1. Verify Foreign Key Column Data Types and Character Sets medium

Ensure the referenced columns in both tables have identical data types and character sets.

1

Identify the columns involved in the foreign key constraint. The error message usually indicates the table and constraint name.

2

Examine the data types and character sets of the columns in the referencing table (the one where you are trying to add the FK) and the referenced table (the one the FK points to).

SHOW CREATE TABLE your_referencing_table;
SHOW CREATE TABLE your_referenced_table;

3

If there are discrepancies in data types (e.g., INT vs. BIGINT, VARCHAR with different lengths) or character sets/collations (e.g., utf8mb4 vs. latin1), you need to alter one of the tables to match the other.

ALTER TABLE your_referencing_table MODIFY COLUMN your_column_name INT UNSIGNED NOT NULL;
-- Or to match character set/collation:
ALTER TABLE your_referencing_table MODIFY COLUMN your_column_name VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL;

4

After ensuring the column definitions are identical, re-attempt to add the foreign key constraint.

ALTER TABLE your_referencing_table ADD CONSTRAINT fk_name FOREIGN KEY (your_column_name) REFERENCES your_referenced_table(referenced_column_name) ON DELETE CASCADE ON UPDATE CASCADE;

2. Check for Missing or Mismatched Indexes easy

Foreign key constraints require an index on the referencing column(s).

1

Determine which columns are part of the foreign key constraint.

2

Check if an index exists on the column(s) in the referencing table. MySQL typically creates one automatically, but it might be missing or corrupted.

SHOW INDEX FROM your_referencing_table;

3

If no index is found, or if the existing index is on a different set of columns, create a new index.

CREATE INDEX idx_your_column_name ON your_referencing_table (your_column_name);

4

Re-attempt to add the foreign key constraint.

ALTER TABLE your_referencing_table ADD CONSTRAINT fk_name FOREIGN KEY (your_column_name) REFERENCES your_referenced_table(referenced_column_name);

3. Review FOREIGN KEY Constraint Options easy

Ensure that `ON DELETE` and `ON UPDATE` actions are valid and correctly specified.

1

Examine the `FOREIGN KEY` clause in your `ALTER TABLE` statement.

ALTER TABLE your_referencing_table ADD CONSTRAINT fk_name FOREIGN KEY (your_column_name) REFERENCES your_referenced_table(referenced_column_name) ON DELETE <action> ON UPDATE <action>;

2

Verify that `<action>` is one of the allowed options: `CASCADE`, `SET NULL`, `RESTRICT`, `NO ACTION`, or `DEFAULT` (for `ON DELETE` only). Ensure there are no typos or invalid keywords.

3

If `SET NULL` is used, ensure that the referencing column(s) are nullable. If the column is `NOT NULL`, you cannot use `SET NULL`.

SHOW CREATE TABLE your_referencing_table;

4

Correct any invalid options or ensure column nullability before re-adding the constraint.

ALTER TABLE your_referencing_table ADD CONSTRAINT fk_name FOREIGN KEY (your_column_name) REFERENCES your_referenced_table(referenced_column_name) ON DELETE CASCADE ON UPDATE CASCADE;

4. Inspect and Correct Parent Table (Referenced Table) Definition medium

Ensure the referenced columns in the parent table are part of a primary key or a unique index.

1

Identify the referenced table and its columns specified in the `REFERENCES` clause of your foreign key definition.

2

Examine the definition of the referenced table to confirm that the referenced columns are either a `PRIMARY KEY` or have a `UNIQUE` index.

SHOW CREATE TABLE your_referenced_table;

3

If the referenced columns are not a primary key or unique index, you must create one. This is a fundamental requirement for foreign keys.

ALTER TABLE your_referenced_table ADD PRIMARY KEY (referenced_column_name);
-- OR
CREATE UNIQUE INDEX idx_unique_referenced_column ON your_referenced_table (referenced_column_name);

4

After ensuring the referenced columns are properly indexed, re-attempt to add the foreign key constraint to the child table.

ALTER TABLE your_referencing_table ADD CONSTRAINT fk_name FOREIGN KEY (your_column_name) REFERENCES your_referenced_table(referenced_column_name);

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Related Errors

5 related errors

MySQL Error 1825: Incorrect Foreign Key Options