# Hello World

This topic demonstrates how you can:

* [Clone](#clone) the mapd-connector repository.
* [Connect](#connect) to a HEAVY.AI server instance.
* [Retrieve](#retrieve) the results of a SQL query.
* [Display](#display) the results on an HTML page.

## Clone

Much of the underlying infrastructure you need to interact with a HEAVY.AI server is provided by the `mapd-connector` repository. You can clone the repository locally to take advantage of its utilities.

To clone the `mapd-connector` repository:

1. Go to [https://github.com/heavyai/mapd-connector](https://github.com/omnisci/mapd-connector).
2. Click **Clone or Download**.
3. Choose whether to clone the repository using HTTPS or SSH, or optionally download a Zip archive to expand on your local drive.

For more information on cloning GitHub repositories, see <https://help.github.com/articles/cloning-a-repository/>

Open `mapd-connector/examples/browser.html` in a web browser to connect to a sample HEAVY.AI server instance and display information from the sample database. You can open `mapd-connector/examples/browser.js` in a text editor and follow along as the following sections describe how the script connects, retrieves, and displays data from the HEAVY.AI server.

## Connect

The lynchpin of the application is establishing a connection to HEAVY.AI. Fortunately, the `MapdCon` object does the heavy lifting for you. You provide the location and port of the HEAVY.AI host and your user credentials to create a connection.

```
const connector = new window.MapdCon()

connector
  .protocol("https")
  .host("metis.mapd.com")
  .port("443")
  .dbName("heavyai")
  .user("admin")
  .password("HyperInteractive")
  .connectAsync()

```

## Retrieve

Connecting to the HEAVY.AI server is not the final goal, of course. Once you have a connection, you can send SQL queries to retrieve data.

First, create constant variables for your SQL queries.

```
// The total number of tweets from Columbia
const query = "SELECT count(*) AS n FROM tweets_nov_feb WHERE country='CO'"
// try changing airtime to arrdelay in the query
const query2 =
  "SELECT carrier_name as key0, AVG(airtime) AS val FROM flights_donotmodify WHERE airtime IS NOT NULL GROUP BY key0 ORDER BY val DESC LIMIT 100"
```

Create an empty array for your query options.

```
const defaultQueryOptions = {}
```

Connect as shown above.

```
const connector = new window.MapdCon()

connector
  .protocol("https")
  .host("metis.mapd.com")
  .port("443")
  .dbName("heavyai")
  .user("admin")
  .password("HyperInteractive")
  .connectAsync()
```

Use a promise to send a series of queries, including the ones defined as constants.

```
  .then(session =>
    // now that we have a session open we can make some db calls:
    Promise.all([
      session.getTablesAsync(),
      session.getFieldsAsync("flights_donotmodify"),
      session.queryAsync(query, defaultQueryOptions),
      session.queryAsync(query2, defaultQueryOptions)
    ])
  )
```

## Display

Promise returns a `values` object with an array of query results. The first item in the `values` array is a list of tables. Write the results to the browser console.

```
  .then(values => {
    console.log(
      "All tables available at metis.mapd.com:",
      values[0].map(x => x.name)
    )
```

The second item in the array contains a list of fields in the table `flights_donotmodify`.

```
    // handle result of getFieldsAsync
    console.log(
      "All fields for 'flights_donotmodify':",
      values[1].reduce((o, x) => Object.assign(o, { [x.name]: x }), {})
    )
```

The third query contains a count of Twitter™ tweets from Columbia. Display that in the HTML page using the DOM.

```
    // handle result of first query
    document.getElementById("result-async").innerHTML =
      "There are " + values[2][0].n + " tweets from Columbia."
    console.log("Query 1 results:", Number(values[2][0].n))
```

The final query returns the average air time for flights listed in the `flights_donotmodify` table, with a limit of 100 records. Display the results as a chart using the createRowChart method.

```
    // handle result of 2nd query
    createRowChart(values[3])
    console.log(
      "Query 2 results:",
      values[3].reduce((o, x) => Object.assign(o, { [x.key0]: x.val }), {})
    )
  })
  .catch(error => {
    console.error("Something bad happened: ", error)
  })
```

Use the array to create a chart using the D3 API. This example is based on an example from the free ebook [D3 Tips and Tricks](https://leanpub.com/D3-Tips-and-Tricks)

```
function createRowChart(data) {
  var margin = { top: 20, right: 20, bottom: 150, left: 40 },
    width = 600
  height = 300

  var x = d3.scale.ordinal().rangeRoundBands([0, width], 0.05)

  var y = d3.scale.linear().range([height, 0])

  var xAxis = d3.svg
    .axis()
    .scale(x)
    .orient("bottom")
    .tickFormat(function(d, i) {
      return d
    })

  var yAxis = d3.svg
    .axis()
    .scale(y)
    .orient("left")
    .ticks(10)

  var svg = d3
    .select("#chart")
    .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")")

  x.domain(
    data.map(function(d) {
      return d.key0
    })
  )
  y.domain([
    0,
    d3.max(data, function(d) {
      return d.val
    })
  ])

  svg
    .append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis)
    .selectAll("text")
    .style("text-anchor", "end")
    .attr("dx", "-.8em")
    .attr("dy", "-.55em")
    .attr("transform", "rotate(-90)")

  svg
    .append("g")
    .attr("class", "y axis")
    .call(yAxis)
    .append("text")
    .attr("transform", "rotate(-90)")
    .attr("y", 6)
    .attr("dy", ".71em")
    .style("text-anchor", "end")

  svg
    .selectAll("bar")
    .data(data)
    .enter()
    .append("rect")
    .style("fill", "steelblue")
    .attr("x", function(d) {
      return x(d.key0)
    })
    .attr("width", x.rangeBand())
    .attr("y", function(d) {
      return y(d.val)
    })
    .attr("height", function(d) {
      return height - y(d.val)
    })
}
```

![](https://1128335264-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6xvZtvY4UaNnTQRXqbwd%2Fuploads%2Fgit-blob-defd4b651831b059a7723b75cddbb0946e205864%2F2_hello_mapd.png?alt=media)