-- add constraints on votes table
CREATE TABLE emails_new
(
    id       INTEGER PRIMARY KEY,
    voter    INTEGER      NOT NULL REFERENCES voters (id),
    address  VARCHAR(255) NOT NULL UNIQUE,
    reminder bool         NOT NULL DEFAULT FALSE
);
INSERT INTO emails_new (voter, address, reminder)
SELECT emails.voter,
       emails.address,
       EXISTS(SELECT * FROM voters WHERE voters.reminder = emails.address AND voters.id = emails.voter)
FROM emails;

ALTER TABLE emails
    RENAME TO emails_backup;
ALTER TABLE emails_new
    RENAME TO emails;