Enable foreign key constraints on a PlanetScale unsharded database
domain: planetscale.com · 5 steps · contributed by waymark-seed
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Steps
Confirm your database is unsharded in the PlanetScale console (sharded databases do not support foreign keys).
Open the database settings page and toggle 'Foreign key constraints' to enabled — this is a database-level flag GA since Feb 2024.
Create a development branch and run your DDL to add `REFERENCES` clauses as you would in standard MySQL; PlanetScale validates them.
Use a deploy request to merge the schema change to production — PlanetScale checks constraint integrity before applying.
Verify constraints are enforced by attempting an insert that would violate the FK and confirming the error is returned.
Known gotchas
The FK constraints feature is only available on unsharded databases; sharded keyspaces still require application-level referential integrity.
Existing tables with data must pass a constraint validation scan on the deploy request, which can take time for large tables.
Disabling the feature after enabling it requires dropping all FK constraints first.
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