# Flyway — Version Control for Your Database

> Flyway is a database migration tool that makes schema changes reliable and repeatable across all environments. It supports over 20 databases and runs migrations from SQL files or Java classes via CLI, Maven, Gradle, or API.

## Install

Save as a script file and run:

# Flyway — Version Control for Your Database

## Quick Use
```bash
# Install via Homebrew
brew install flyway

# Or download from the official site
# Create a migration file
mkdir -p sql
cat > sql/V1__create_users.sql <<EOF
CREATE TABLE users (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) UNIQUE
);
EOF

# Run migrations
flyway -url=jdbc:mysql://localhost:3306/mydb -user=root -password=secret migrate
```

## Introduction
Flyway brings version control discipline to database schemas. Each migration is a versioned SQL file that Flyway applies in order, tracking which migrations have run in a metadata table. This ensures every environment — development, staging, production — has an identical schema without manual intervention.

## What Flyway Does
- Applies versioned SQL or Java migrations in sequential order with automatic conflict detection
- Tracks applied migrations in a schema history table for audit and rollback awareness
- Validates that previously applied migrations have not been modified to prevent drift
- Supports repeatable migrations for views, procedures, and reference data that change over time
- Provides baseline support to adopt Flyway on existing databases without re-running history

## Architecture Overview
Flyway reads migration files from a configured location, sorts them by version number, and compares them against the schema history table in the target database. Pending migrations are executed in a transaction where the database supports transactional DDL. After each migration, a checksum is stored so Flyway can detect unauthorized modifications on future runs. The tool connects via JDBC drivers for broad database compatibility.

## Self-Hosting & Configuration
- Available as a standalone CLI, Docker image, or plugin for Maven, Gradle, and SBT
- Configure via flyway.conf file, environment variables, or command-line arguments
- Set locations to point to SQL migration directories, classpaths, or cloud storage
- Use placeholders for environment-specific values like schema names or table prefixes
- Enable callbacks for pre- and post-migration hooks for custom logic

## Key Features
- Checksum validation ensures migration integrity across all environments
- Undo migrations (Teams edition) allow controlled rollback of applied changes
- Dry-run mode previews SQL that would be executed without applying it
- Cherry-pick specific migrations to apply or skip during targeted deployments
- Native integration with Spring Boot auto-configuration for Java applications

## Comparison with Similar Tools
- **Liquibase** — XML/YAML/JSON changeset model; more flexible formats but steeper learning curve
- **golang-migrate** — Lightweight Go CLI and library; fewer database drivers and no checksum validation
- **Atlas** — Declarative schema approach with drift detection; newer with smaller ecosystem
- **dbmate** — Simple Go tool focused on SQL migrations; no Java integration or checksum tracking
- **Alembic** — Python-based migration tool tied to SQLAlchemy; best for Python-only projects

## FAQ
**Q: Does Flyway support rollbacks?**
A: The Community edition supports manual rollback via custom down scripts. The Teams edition adds automated undo migrations.

**Q: Can I use Flyway with NoSQL databases?**
A: Flyway is designed for relational databases accessed via JDBC. It supports MongoDB in newer versions with limited features.

**Q: How do I handle migration conflicts in a team?**
A: Use the outOfOrder option to allow later-versioned migrations to run even if earlier ones were added after deployment.

**Q: Is there a GUI for Flyway?**
A: Flyway Desktop provides a visual interface for comparing schemas, generating migrations, and managing baselines.

## Sources
- https://github.com/flyway/flyway
- https://documentation.red-gate.com/flyway

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Source: https://tokrepo.com/en/workflows/d3247e04-3abd-11f1-9bc6-00163e2b0d79
Author: Script Depot