Dev

Mock Database Migration Generator

The mock database migration generator produces ready-to-run SQL migration scripts with both UP and DOWN sections, covering the most common schema operations across PostgreSQL, MySQL, and SQLite. Whether you're scaffolding a new table, adding a nullable column, or building an index on a foreign key, getting the exact syntax right for each dialect takes time you don't always have. This tool removes that friction. Each generated script follows the same structure that migration frameworks expect: a clearly labeled UP block that applies the change and a DOWN block that reverses it cleanly. That symmetry is what makes migrations safe to run in CI pipelines and easy to roll back in staging environments. The generator supports three SQL dialects — PostgreSQL, MySQL, and SQLite — and produces dialect-specific syntax for data types, quoting, and constraint definitions. A PostgreSQL CREATE TABLE uses SERIAL and TEXT where MySQL would use INT AUTO_INCREMENT and VARCHAR, and the output reflects those differences automatically. Common use cases include generating test fixtures for tools like Flyway or Knex.js, building documentation examples that show real SQL instead of pseudocode, and giving junior developers a correct starting point they can adapt rather than write from scratch. Fill in the table name, pick the operation type, choose your dialect, and get a script you can paste directly into your migrations folder.

How to Use

  1. Enter the exact table name you want to target in the Table Name field (e.g., 'orders' or 'user_profiles').
  2. Select the migration type from the dropdown — choose create-table, add-column, drop-column, rename-column, or create-index.
  3. Pick the SQL dialect that matches your database: PostgreSQL, MySQL, or SQLite.
  4. Click Generate to produce the migration script, then review the UP and DOWN sections for correctness.
  5. Copy the output and paste it into your migration file, adjusting column types or constraints to match your real schema.

Use Cases

  • •Generating a PostgreSQL CREATE TABLE script with a matching DROP TABLE rollback
  • •Scaffolding an ADD COLUMN migration for MySQL before writing the actual ORM model
  • •Creating a DROP COLUMN script pair to test rollback logic in a CI pipeline
  • •Producing SQLite migrations for a mobile app's local database schema versioning
  • •Building code examples for internal wikis documenting schema change conventions
  • •Seeding a migration folder with placeholder scripts during early project setup
  • •Testing Flyway or Liquibase runner configurations against known-good SQL scripts
  • •Demonstrating UP/DOWN migration patterns to developers new to schema versioning

Tips

  • →When using create-table, immediately generate a matching create-index script for the same table to scaffold both files at once.
  • →For Flyway projects, generate the DOWN script as a separate undo migration file prefixed with U instead of V.
  • →SQLite's DROP COLUMN output should be tested against your SQLite version — versions below 3.35.0 require a table-rebuild workaround instead.
  • →Use the rename-column operation to generate the syntax reference, then manually add a data migration step if the column holds values that need transforming.
  • →MySQL users: the generated scripts assume InnoDB; add ENGINE=InnoDB explicitly if your database defaults to MyISAM to ensure transaction support.
  • →Generate the same operation in all three dialects and diff the output to build a personal reference for cross-database syntax differences.

FAQ

What is the difference between a migration UP and DOWN script?

The UP script applies a schema change — creating a table, adding a column, or building an index. The DOWN script reverses that exact change, dropping the table, removing the column, or deleting the index. Keeping them in sync means you can roll back to any previous schema state without manual SQL, which is critical for staging deployments and hotfix rollbacks.

Which migration frameworks can use these generated SQL scripts?

The output works with Flyway and Liquibase (both accept raw SQL files), Knex.js migrations (paste into the up/down functions), Golang Migrate, and any custom runner that executes plain SQL. The scripts don't use framework-specific DSLs, so they're portable across tools as long as the dialect matches your database.

How do PostgreSQL, MySQL, and SQLite migration scripts differ?

PostgreSQL uses SERIAL for auto-increment primary keys and supports RETURNING clauses. MySQL uses INT AUTO_INCREMENT and requires ENGINE=InnoDB for transactions. SQLite has limited ALTER TABLE support — it can't drop columns in older versions — so DROP COLUMN scripts may need workarounds. The generator produces dialect-correct syntax for each, reflecting these real differences.

Can I use these migration scripts directly in production?

Treat them as a strong starting point, not a final artifact. Review the generated column types and constraints against your actual data requirements — for example, a VARCHAR length or NOT NULL constraint may need adjusting. Always test UP and DOWN scripts on a staging database before running them in production.

What migration operations does this generator support?

The generator covers the most common schema operations: creating a new table, adding a column to an existing table, dropping a column, renaming a column, and creating an index. These cover roughly 90% of everyday migration work. Complex operations like changing a column's data type or adding foreign key constraints would need manual additions.

How should I name my migration files when using these scripts?

Most migration tools expect a timestamp or version prefix followed by a description, such as 20240610_001_add_email_to_users.sql or V3__create_orders_table.sql. Flyway uses the V prefix convention; Liquibase supports both. The table name and operation you specify in this generator map naturally to the descriptive part of the filename.

Does SQLite support all the same migration operations as PostgreSQL?

No. SQLite's ALTER TABLE is significantly limited. Before version 3.35.0, SQLite did not support DROP COLUMN at all. Renaming columns was added in 3.25.0. If you're targeting older SQLite versions, the standard workaround is to create a new table with the desired schema, copy the data, drop the old table, and rename the new one.

How do I add these scripts to an existing Knex.js or Sequelize project?

In Knex.js, run knex migrate:make migration_name to create the file, then paste the UP script body into the exports.up function wrapped in knex.raw() and the DOWN script into exports.down. For Sequelize, use sequelize migration:generate and paste into the up and down methods similarly, also wrapped in queryInterface.sequelize.query().