quiz grouping

migrations/0061_quiz_target_year.down.sql

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+ALTER TABLE quizzes DROP COLUMN IF EXISTS target_year;

migrations/0061_quiz_target_year.up.sql

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+-- The year of a lecture or conversation a quiz is attached to, captured when
+-- the quiz is saved, so the app can group quizzes by year without looking
+-- each transcript up. NULL for chapters, stand-alone quizzes, and undated
+-- recordings.
+ALTER TABLE quizzes ADD COLUMN IF NOT EXISTS target_year SMALLINT;