Demo code problem
https://github.com/chenshenhai/koa2-note/blob/c667c4fa4b9cf31acd2b76e29a5056b69581ca65/demo/project/server/utils/db-util.js#L17

The code here is `reject ` but not `resolve `

```
return new Promise(( resolve, reject ) => {
    pool.getConnection(function(err, connection) {
      if (err) {
        resolve( err ) // reject( err )
      } else {
        connection.query(sql, values, ( err, rows) => {
          if ( err ) {
            reject( err )
          } else {
            resolve( rows )
          }
          connection.release()
        })
      }
    })
  })
```