-- add constraints on votes table
CREATE TABLE votes_new
(
    decision INTEGER  NOT NULL REFERENCES decisions (id),
    voter    INTEGER  NOT NULL REFERENCES voters (id),
    vote     INTEGER  NOT NULL,
    voted    DATETIME NOT NULL,
    notes    TEXT     NOT NULL DEFAULT '',
    PRIMARY KEY (decision, voter)
);
INSERT INTO votes_new (decision, voter, vote, voted, notes)
SELECT decision,
       voter,
       vote,
       voted,
       notes
FROM votes
GROUP BY decision, voter
HAVING MAX(voted) = voted;

ALTER TABLE votes
    RENAME TO votes_orig_with_duplicates;
ALTER TABLE votes_new
    RENAME TO votes;