CREATE TABLE config_revision_preview (
    revision_id   TEXT NOT NULL PRIMARY KEY REFERENCES config_revision (id) ON DELETE CASCADE,
    fragments     TEXT NOT NULL DEFAULT '{}'
);

INSERT INTO config_revision_preview (revision_id, fragments)
SELECT id, json(COALESCE(json_extract(meta_json, '$.preview_fragments'), '{}'))
FROM config_revision
WHERE json_extract(meta_json, '$.preview_fragments') IS NOT NULL;

UPDATE config_revision
SET meta_json = json_remove(meta_json, '$.preview_fragments')
WHERE json_extract(meta_json, '$.preview_fragments') IS NOT NULL;