Database engine
the SQL dialect and feature setNeon is full Postgres 16/17 with extensions: pgvector for embeddings, PostGIS for geospatial, pg_partman for partitioning, plv8, citext, etc. Anything you can do on a self-hosted Postgres works here. The protocol is standard, so any Postgres client (Prisma, Drizzle, raw pg) connects natively.
PlanetScale is MySQL 8 on Vitess. Most MySQL features are available, but with Vitess constraints: no foreign keys (enforced application-side), no cross-shard transactions, certain JOINs require care to stay performant. The Vitess query rewriting handles a lot of this transparently, but it's not 100% transparent.
If your team writes Postgres in muscle memory, Neon is the path of least resistance. If you're MySQL-shaped and at scale, PlanetScale's Vitess foundation is genuinely valuable. The choice between Postgres and MySQL is more about ecosystem familiarity than technical superiority.