This error appears when you try to drop or rename a column that is referenced by a generated column in the same table.
ER_DEPENDENT_BY_GENERATED_COLUMN occurs in MySQL when you attempt to drop or rename a column that another generated column depends on. Redefine or remove the dependent generated column first, then retry the DDL statement.
ER_DEPENDENT_BY_GENERATED_COLUMN
MySQL raises error 3108 with SQLSTATE HY000 when a DDL statement attempts to drop or rename a column that is referenced by another generated column. The server blocks the operation to maintain data consistency.
The problem appears mostly during schema refactoring when tables contain generated columns created with the GENERATED ALWAYS AS syntax. Because generated columns compute their value from other columns, deleting a source column would break the expression.
Resolving the error quickly matters because failed migrations halt deployments, affect CI pipelines, and create downtime in production environments.
The root cause is an explicit dependency graph maintained by MySQL between generated columns and their source columns. When you try to ALTER TABLE to drop or rename a source column, the engine detects the relationship and throws ER_DEPENDENT_BY_GENERATED_COLUMN.
Additional triggers include renaming columns used inside a generated column expression, using CASCADE constraints without adjusting generated columns, and importing an old schema snapshot lacking generated-column definitions.
Fix the error in two steps: first drop or redefine the generated column so it no longer references the target column, then rerun the original ALTER TABLE statement.
Optionally, create a temporary generated column that uses the new column name, populate data if needed, and finally drop the obsolete generated column. Version-control each step to keep migrations incremental and reversible.
Schema migrations often rename a measurement column (e.g., gross_price to list_price) while a generated column computes net_price = gross_price - discount. Dropping gross_price triggers the error. The fix is to drop net_price first or rewrite it to use list_price.
Another scenario involves ORMs that auto-generate ALTER TABLE statements during model sync. Always review generated migrations for hidden dependencies on generated columns before applying them.
Document every generated column with comments indicating its dependencies. Use Galaxy collections to store vetted DDL scripts so teammates see the dependency chain before editing schema.
Automate schema diffs in CI to detect generated-column dependencies. Naming conventions like prefixing generated columns with g_ can also alert reviewers.
ER_GENERATED_COLUMN_REF_AUTO_INC prohibits generated columns from referencing auto-increment columns. ER_BAD_FIELD_ERROR appears if a generated column references a non-existent column after an incorrect rename. Fixes follow the same pattern: adjust or drop the generated column, then retry the DDL.
The column being dropped is directly referenced in a GENERATED ALWAYS AS expression.
The column is renamed without simultaneously updating the generated column definition.
The generated column was created in a later migration that teammates overlooked during cleanup.
ORM auto-migration tools generated ALTER TABLE statements out of order, leaving dependent columns intact.
Triggered when a generated column references an auto-increment column. Solve by removing the reference or disabling auto-increment.
Occurs when SQL references a column that does not exist, often after an incomplete rename. Verify column names and generated column expressions.
Similar to 1054 but surfaces during SELECT or UPDATE. Adjust queries or recreate missing columns.
Dropping the source column would invalidate the generated column expression, risking inconsistent data, so MySQL prevents the operation.
No. MySQL enforces the check for data integrity. You must adjust or remove the generated column first.
Yes. The dependency rule covers both STORED and VIRTUAL generated columns.
Galaxy surfaces schema metadata and warns you in the editor when a generated column depends on the target column, reducing surprise failures during migration.
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