CREATE TABLE change_tag (
  ct_rc_id   INTEGER      NULL,
  ct_log_id  INTEGER      NULL,
  ct_rev_id  INTEGER      NULL,
  ct_tag     TEXT     NOT NULL,
  ct_params  TEXT         NULL
);
CREATE UNIQUE INDEX change_tag_rc_tag ON change_tag(ct_rc_id,ct_tag);
CREATE UNIQUE INDEX change_tag_log_tag ON change_tag(ct_log_id,ct_tag);
CREATE UNIQUE INDEX change_tag_rev_tag ON change_tag(ct_rev_id,ct_tag);
CREATE INDEX change_tag_tag_id ON change_tag(ct_tag,ct_rc_id,ct_rev_id,ct_log_id);