table_exists = async (db, tblname) => {
  const { rows } = await db.query(`SELECT EXISTS
    (
        SELECT 1
        FROM information_schema.tables
        WHERE table_schema = 'public'
        AND table_name = '${tblname}'
    );`);
  return rows[0].exists;
}
@param {object} db
@param {string} tblname
@returns {Promise<boolean>}