Gmail to SQLite(github.com)

  CREATE TABLE IF NOT EXISTS "messages" (
    "id" INTEGER NOT NULL PRIMARY KEY, -- internal id
    "message_id" TEXT NOT NULL, -- Gmail message id
    "thread_id" TEXT NOT NULL, -- Gmail thread id
    "headers" JSON NOT NULL, -- JSON object of { "header": value },
    "subject" TEXT GENERATED ALWAYS AS (json_extract("headers", '$.Subject')) VIRTUAL NOT NULL)
    ...
  );
  CREATE INDEX subjectidx on messages(subject);

  ALTER TABLE messages ADD dkim TEXT GENERATED ALWAYS AS (json_extract("headers", '$."Dkim-Signature"')) VIRTUAL NOT NULL);
  CREATE INDEX dkimidx on messages(dkim);
  SELECT dkim, COUNT(0) FROM messages GROUP BY dkim;