DROP COLUMN or DROP INDEX is run on an already-dropped column or index (non-idempotent migration). The column or index name has a typo in the migration script. The migration was applied to one environment but the target environment is at a different schema version

Step 1: Verify the column or index exists: `SHOW COLUMNS FROM your_table;` and `SHOW INDEX FROM your_table;`. Step 2: Use migration tools (Flyway or Liquibase) that track applied migrations to prevent re-running DROP statements.. Step 3: Skip the migration if the column/key is already gone and mark it as applied in your migration tracker.

Low severityschema

Power BI Refresh Error:
1091

What does this error mean?

An ALTER TABLE DROP COLUMN or DROP INDEX statement references a column or index that does not exist.

Common causes

1DROP COLUMN or DROP INDEX is run on an already-dropped column or index (non-idempotent migration)
2The column or index name has a typo in the migration script
3The migration was applied to one environment but the target environment is at a different schema version

How to fix it

1Step 1: Verify the column or index exists: `SHOW COLUMNS FROM your_table;` and `SHOW INDEX FROM your_table;`
2Step 2: Use migration tools (Flyway or Liquibase) that track applied migrations to prevent re-running DROP statements.
3Step 3: Skip the migration if the column/key is already gone and mark it as applied in your migration tracker.

Frequently asked questions

How do I safely drop a column that may or may not exist in MySQL?

MySQL does not support DROP COLUMN IF EXISTS natively. Write a stored procedure that queries information_schema.columns and conditionally executes the DROP.

What migration tools handle idempotency automatically for MySQL?

Flyway and Liquibase both track which migrations have been applied and will not re-run them, preventing this error class entirely.

Can MetricSign detect schema migration failures in my data pipelines?

Yes — when a migration failure causes ADF or dbt to fail, MetricSign surfaces the incident with the specific MySQL error code.

Official documentation: https://dev.mysql.com/doc/mysql-errors/8.0/en/server-error-reference.html