callback-vs-promise.js

client.query('SELECT NOW() as now', (err, res) => {
  if (err) {
    console.log(err.stack)
  } else {
    const targetDate = res.rows[0];
    client.query(`SELECT * from myTable where lastCreated > ${res.rows[0]}`, (er2, res2) => {
      //This, in theory could go on a bit. Note that this is a contrived example and in the case
      // of SQL, you'd use the proper joins and conditionals in one statement. 
    })
  }
})

// promise
client.query('SELECT NOW() as now')
  .then(res => console.log(res.rows[0]))
  .catch(e => console.error(e.stack))