Flyway is a database migration tool that applies versioned SQL (or Java-based) migration scripts in strict numerical order — each script is named following a convention like `V1__create_users_table.sql`, `V2__add_email_column.sql` — and tracks which migrations have already been applied in a dedicated schema history table (`flyway_schema_history`), so on startup it only runs the migrations that haven't been applied yet, ensuring the schema evolves predictably and identically across every environment.

Intermediate5 min

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#Flyway#Database Migration

What is Flyway, and how does it manage database schema changes?

Already-Applied Migrations Are Effectively Immutable

Once a migration script has been applied in any shared environment, Flyway checksums it and will refuse to run (by default) if that already-applied script's content is later edited — this is a deliberate safety guarantee: schema history must be an append-only, trustworthy record of exactly what was run, so fixing a mistake in an already-applied migration means writing a NEW migration script to correct it, not editing the old one.

V1__create_users.sql, V2__add_email.sql, ... — Flyway applies them in strict order, tracked in flyway_schema_history, once each

Flyway Migration Script

java

-- V2__add_email_column.sql
ALTER TABLE users ADD COLUMN email VARCHAR(255) NOT NULL DEFAULT '';