What is Database Migration?

A database migration changes tables, columns, indexes, constraints, and sometimes data through versioned steps. The goal is to keep the database schema aligned with what the application code expects.

How It Works

Each change is recorded as a migration file: adding a column, changing a column type, creating an index, splitting a table, or setting a default value. These files run in order across development, staging, and production. Migration tools track which files have already been applied in a separate table.

Tools such as Prisma, Drizzle, Rails, Django, and Flyway can manage schema migration. With an ORM such as Prisma, migration files make the difference between model definitions and the database visible.

Production Concerns

On large tables, locking ALTER TABLE statements can cause downtime. Larger changes are often split into smaller backward-compatible steps: add the new column, make the application support both fields, backfill data in the background, then remove the old column. This is commonly called an expand-contract approach.

Migration in a database context is not just moving files; it requires backups, rollback planning, schema review, and monitoring. During an ORM migration, automatically generated SQL should be reviewed for production impact.