Postgres → MySQL Migration

Going from Postgres to MySQL is a downgrade in feature set. Plan for what you'll lose (JSONB-style operators, array columns, partial indexes, rich CHECK constraints, generated columns until 8.0, true sequences) and design around it.

The opinion

Don't do this unless forced. Postgres is the Rails-community default for good reason. If forced (vendor mandate, hosting choice, cost), use pgloader for the bulk migration, dual-write during cutover, and audit every column-type-specific feature in the schema before flipping.

Counter-position: MySQL 8.0+ has closed many gaps (JSON functions, generated columns, CHECK constraints enforced). For simple Rails schemas, the migration is straightforward. The complexity is per-feature.

Pre-migration audit

# Catalog every Postgres-specific feature in your schema
grep -E "jsonb|ARRAY|generated as identity|::regclass|@>|<@|tsvector" db/structure.sql