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Description

This error occurs when you attempt to create a foreign key constraint, but the column specified in the `REFERENCES` clause does not exist in the referenced (parent) table. It typically indicates a structural mismatch between your intended foreign key definition and the parent table's schema, preventing the constraint from being added.

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Error Message

Failed to add the foreign key constraint. Missing column '%s' for constraint '%s' in the referenced table '%s'

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Known Causes

4 known causes

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Typo in Referenced Column Name

A spelling mistake or incorrect casing in the column name specified within the `REFERENCES` clause prevents MySQL from finding the corresponding column in the parent table.

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Referenced Column Not Yet Defined

The column intended to be the primary key or unique key in the parent table, which the foreign key should reference, has not actually been created in that table.

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Referencing Incorrect Parent Table

The `REFERENCES` clause points to an incorrect parent table, which does not contain the expected column for the foreign key, or the table name itself is misspelled.

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Case Sensitivity Mismatch

On systems configured for case-sensitive database object names, the casing of the column name in the foreign key definition does not exactly match the actual column name in the referenced table.

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Solutions

4 solutions available

1. Verify Referenced Column Existence and Data Type easy

Ensure the column you're referencing in the parent table actually exists and has a compatible data type.

1

Identify the table and column that the foreign key is trying to reference. The error message will provide the table name (e.g., '%s' in the error message).

2

Connect to your MySQL database and describe the structure of the referenced table.

DESCRIBE referenced_table_name;

3

Check if the column specified in the foreign key definition (the one that should be referenced) exists in the output of the DESCRIBE command.

4

If the column exists, verify that its data type is compatible with the column in the child table that you are using for the foreign key. For example, you cannot reference an INT column with a VARCHAR column directly without a conversion or a matching type.

5

If the column is missing or has an incompatible data type, you will need to either add the missing column to the referenced table or modify the foreign key definition to reference an existing, compatible column.

2. Correct Foreign Key Definition easy

Adjust the `FOREIGN KEY` constraint definition to accurately point to an existing column in the referenced table.

1

Locate the `ALTER TABLE` statement or `CREATE TABLE` statement where the foreign key constraint is being defined.

2

Examine the `REFERENCES` clause of the foreign key definition. It should specify the correct referenced table and the correct column within that table.

CONSTRAINT constraint_name
FOREIGN KEY (child_column_name)
REFERENCES referenced_table_name (referenced_column_name);

3

Ensure that `referenced_column_name` in the `REFERENCES` clause is an actual column name that exists in `referenced_table_name`.

4

If the `referenced_column_name` is incorrect, modify it to match the actual column name in the referenced table. Pay close attention to spelling and case sensitivity.

5

Re-execute the `ALTER TABLE` or `CREATE TABLE` statement with the corrected foreign key definition.

ALTER TABLE child_table_name
ADD CONSTRAINT constraint_name
FOREIGN KEY (child_column_name)
REFERENCES referenced_table_name (correct_referenced_column_name);

3. Add Missing Referenced Column medium

If the referenced column is genuinely missing, add it to the parent table.

1

Determine the correct data type for the missing column. It should ideally match the data type of the column in the child table that will be used for the foreign key.

2

Connect to your MySQL database.

3

Add the missing column to the referenced table. Use an `ALTER TABLE` statement.

ALTER TABLE referenced_table_name
ADD COLUMN missing_column_name data_type [constraints];

4

If the child table already has data, you might need to populate the newly added column in the referenced table with appropriate values before or after adding the foreign key constraint. Consider adding a `NOT NULL` constraint if applicable, and provide a default value.

5

Once the column is added and potentially populated, retry adding the foreign key constraint.

ALTER TABLE child_table_name
ADD CONSTRAINT constraint_name
FOREIGN KEY (child_column_name)
REFERENCES referenced_table_name (missing_column_name);

4. Ensure Referenced Column is Indexed medium

While not always the direct cause of this specific error, an unindexed referenced column can lead to performance issues and sometimes manifest in unexpected ways. Ensure it's indexed.

1

Identify the column in the referenced table that the foreign key points to.

2

Check if an index already exists on this column. You can use `SHOW INDEXES FROM referenced_table_name;` or query `information_schema.STATISTICS`.

SHOW INDEXES FROM referenced_table_name;

3

If no index exists on the referenced column, create one.

CREATE INDEX index_name ON referenced_table_name (referenced_column_name);

4

After ensuring the referenced column exists and is indexed, retry adding the foreign key constraint.

ALTER TABLE child_table_name
ADD CONSTRAINT constraint_name
FOREIGN KEY (child_column_name)
REFERENCES referenced_table_name (referenced_column_name);

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Related Errors

5 related errors

MySQL Error 3734: Missing Referenced Foreign Key Column