text: -- Up
  CREATE TABLE Sensor (
      name TEXT PRIMARY KEY,
      firstonline TEXT NOT NULL,
      lastonline TEXT NOT NULL
  );
  CREATE TABLE Reading (
      id INTEGER PRIMARY KEY AUTOINCREMENT,
      sensorname TEXT,
      temperature NUMERIC(10,2),
      pressure NUMERIC(10,2),
      humidity NUMERIC(10,2),
      timestamp TEXT,
      FOREIGN KEY (sensorname) REFERENCES Sensor(name)
  );
  
  -- Down
  DROP TABLE Sensor;
  DROP TABLE Reading;