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Description

This error indicates that a specific expression, function, or construct used within a column's `DEFAULT` clause in a `CREATE TABLE` or `ALTER TABLE` statement is not permitted. MySQL has strict rules about what can be used as a default value, primarily limiting them to literals, `NULL`, or specific time-related functions.

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Error Message

'%s' is not supported for default value expressions.

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Known Causes

3 known causes

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Non-Constant Function Usage

Attempting to use a function (e.g., `UUID()`, `RAND()`) that produces a different result each time it's called as a column's default value.

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Cross-Column Reference

Defining a column's default value by referencing another column within the same table definition, which is generally not allowed.

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Complex Expression

Employing an overly complex expression, a subquery, or a user-defined variable as the default value for a column.

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Solutions

3 solutions available

1. Use a Supported Default Value easy

Replace the unsupported expression with a static, supported value.

1

Identify the column and table causing the error. The error message '%s' will usually point to the specific expression that is not supported.

2

Modify the table schema to remove the unsupported default value. If you are creating a new table, adjust the `DEFAULT` clause. If you are altering an existing table, you will need to drop the existing default and add a new one.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name data_type DEFAULT 'supported_value';
-- Or for creation:
CREATE TABLE your_table_name (
    your_column_name data_type DEFAULT 'supported_value'
);

3

Ensure the 'supported_value' is a literal value (string, number, NULL) or a simple function like `CURRENT_TIMESTAMP` if applicable to your MySQL version and the data type.

2. Migrate Logic to Application Layer medium

Handle the default value generation in your application code instead of the database.

1

Remove the unsupported `DEFAULT` clause from the column definition in your MySQL table schema.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name data_type;
-- Or for creation:
CREATE TABLE your_table_name (
    your_column_name data_type
);

2

In your application's data insertion logic (e.g., in your Python, Java, PHP, Node.js code), generate the required default value before executing the `INSERT` statement.

// Example in Python using SQLAlchemy:
from datetime import datetime

new_record = {
    'your_column_name': datetime.now(), # Or any other logic
    'other_column': 'some_value'
}

session.execute(your_table.insert().values(new_record))

3

Ensure your application code consistently applies this logic for all new records to maintain data integrity.

3. Update MySQL Version advanced

Upgrade to a MySQL version that supports the desired default value expression.

1

Consult the MySQL documentation for your current and target versions to identify which default value expressions are supported. The specific unsupported expression might be supported in newer versions.

2

Plan and execute a MySQL version upgrade. This typically involves backing up your database, installing the new MySQL version, and performing a data migration or upgrade process.

3

After the upgrade, re-apply the `DEFAULT` clause with the desired expression. For example, if `UUID()` was the issue and it's supported in the new version:

ALTER TABLE your_table_name MODIFY COLUMN your_column_name VARCHAR(36) DEFAULT (UUID());
-- Or for creation:
CREATE TABLE your_table_name (
    your_column_name VARCHAR(36) DEFAULT (UUID())
);

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Related Errors

5 related errors

MySQL Error 3774: Unsupported Default Value Expression