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Description

This error occurs when you attempt to define a default value expression for a column that references another column specified as `AUTO_INCREMENT`. MySQL does not permit generated default values to depend on auto-incrementing columns due to potential circular dependencies and unpredictable behavior during row insertion. It typically arises during `CREATE TABLE` or `ALTER TABLE` statements.

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Error Message

Default value expression of column '%s' cannot refer to an auto-increment column.

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Known Causes

3 known causes

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Direct Auto-Increment Reference

Attempting to use the value of an `AUTO_INCREMENT` column within the `DEFAULT` expression of another column in the same table definition.

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Indirect Reference via Function

Employing a SQL function in a `DEFAULT` expression where one of the function's arguments is an `AUTO_INCREMENT` column, leading to an indirect dependency.

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Generated Column Default Conflict

Defining a generated column with a `DEFAULT` expression that relies on an `AUTO_INCREMENT` column, which is not supported by MySQL.

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Solutions

3 solutions available

1. Remove Auto-Increment from Default Value Column easy

The most direct fix is to remove the AUTO_INCREMENT attribute from the column intended for the default value.

1

Identify the column causing the error. This is usually a column that is attempting to use another column's auto-increment value as its default.

2

Modify the table definition to remove the `AUTO_INCREMENT` keyword from the problematic column.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name data_type [constraints];

3

If the column was intended to have a default value that is *not* an auto-increment reference, specify that default value explicitly.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name data_type DEFAULT 'your_default_value';

2. Use a Trigger for Dependent Default Values medium

Implement a trigger to populate the dependent column *after* the auto-increment value has been assigned.

1

Identify the table and the columns involved. You'll need the auto-increment column and the column that was trying to reference it as a default.

2

Create a `BEFORE INSERT` trigger that updates the dependent column with the value of the auto-increment column.

DELIMITER //
CREATE TRIGGER set_dependent_default
BEFORE INSERT ON your_table_name
FOR EACH ROW
BEGIN
    SET NEW.dependent_column_name = NEW.auto_increment_column_name;
END; //
DELIMITER ;

3

Ensure the `dependent_column_name` does not have an `AUTO_INCREMENT` definition itself, and remove any invalid default value expression.

3. Re-evaluate Table Design and Dependencies advanced

Consider if the current table structure is the most appropriate for the intended relationships.

1

Analyze the purpose of the column that is causing the error. Why was it intended to have a default value referencing an auto-increment column?

2

If the intention was to create a sequence or a related identifier, explore alternative database design patterns such as:
- Using a separate sequence table.
- Utilizing a `UUID` for unique identifiers if chronological order is not critical.
- Rethinking the relationship between the tables.

3

If a related ID is needed, consider making the dependent column a foreign key to another table that *does* have an auto-increment primary key.

ALTER TABLE your_table_name ADD COLUMN related_id INT REFERENCES another_table(id);

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Related Errors

5 related errors

MySQL Error 3768: Default Value Auto-Increment Reference