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Caro is thinking out loud

A foreign key is a column in a table linked to a column in a different table

Write foreign key table constraints in a schema like this:

CREATE TABLE "visits" (
  "rider_id" INTEGER,
  "station_id" INTEGER,
  FOREIGN KEY("rider_id") REFERENCES "riders"("id"),
  FOREIGN KEY("station_id") REFERENCES "stations"("id")
)

You might want to specify what happens to these records if the related record is deleted from another table, so you don’t end up with records that don’t reference anything. This would be achieved using ON DELETE , for example ON DELETE SET NULL sets the reference to NULL if the thing referred to is deleted, or ON DELETE CASCADE to delete things referencing the record in another table when that thing is deleted.

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