Square provides a point-of-sale credit card processing system. Chances are you've used its card reader to make purchases at a local small business.

Looker is a powerful, modern business intelligence platform that has become the new standard for how modern enterprises analyze their data. From large corporations to agile startups, savvy companies can leverage Looker's analysis capabilities to monitor the health of their businesses and make more data-driven decisions.

Looker is differentiated from other BI and analysis platforms for a number of reasons. Most notable is the use of LookML, a proprietary language for describing dimensions, aggregates, calculations, and data relationships in a SQL database. LookML enables organizations to abstract the query logic behind their analyses from the content of their reports, making their analytics easy to manage, evolve, and scale.

Square offers multiple APIs, but its Connect API is the best way to pull data from its system. It provides calls for customers, transactions, checkouts, and a handful of other endpoints. To use it to list transactions for a particular location, for example, you would call GET /v2/locations/[location_id]/transactions.

The Square API returns JSON-format data. The data returned for a "list transactions" call might look like this:

{
  "transactions": [
    {
      "id": "KnL67ZIwXCPtzOrqj0HrkxMF",
      "location_id": "18YC4JDH91E1H",
      "created_at": "2017-11-20T22:57:56Z",
      "tenders": [
        {
          "id": "MtZRYYdDrYNQbOvV7nbuBvMF",
          "location_id": "18YC4JDH91E1H",
          "transaction_id": "KnL67ZIwXCPtzOrqj0HrkxMF",
          "created_at": "2017-11-20T22:57:56Z",
          "note": "some optional note",
          "amount_money": {
            "amount": 5000,
            "currency": "USD"
          },
          "processing_fee_money": {
            "amount": 138,
            "currency": "USD"
          },
          "type": "CARD",
          "card_details": {
            "status": "CAPTURED",
            "card": {
              "card_brand": "VISA",
              "last_4": "1111"
            },
            "entry_method": "KEYED"
          },
          "additional_recipients": [
            {
              "location_id": "057P5VYJ4A5X1",
              "description": "Application fees",
              "amount_money": {
                "amount": 20,
                "currency": "USD"
              }
            }
          ]
        }
      ],
      "refunds": [
        {
          "id": "7a5RcVI0CxbOcJ2wMOkE",
          "location_id": "18YC4JDH91E1H",
          "transaction_id": "KnL67ZIwXCPtzOrqj0HrkxMF",
          "tender_id": "MtZRYYdDrYNQbOvV7nbuBvMF",
          "created_at": "2017-11-20T22:59:20Z",
          "reason": "some reason why",
          "amount_money": {
            "amount": 5000,
            "currency": "USD"
          },
          "status": "APPROVED",
          "processing_fee_money": {
            "amount": 138,
            "currency": "USD"
          },
          "additional_recipients": [
            {
              "location_id": "057P5VYJ4A5X1",
              "description": "Application fees",
              "amount_money": {
                "amount": 100,
                "currency": "USD"
              }
            }
          ]
        }
      ],
      "reference_id": "some optional reference id",
      "product": "EXTERNAL_API"
    }
  ]
}

If you don't already have a data structure in which to store the data you retrieve, you'll have to create a schema for your data tables. Then, for each value in the response, you'll need to identify a predefined datatype (INTEGER, DATETIME, etc.) and build a table that can receive them. Square's documentation should tell you what fields are provided by each endpoint, along with their corresponding datatypes.

Complicating things is the fact that the records retrieved from the source may not always be "flat" – some of the objects may actually be lists. This means you'll likely have to create additional tables to capture the unpredictable cardinality in each record.

To perform its analyses, Looker connects to your company's database or data warehouse, where the data you want to analyze is stored. Some popular data warehouses include Amazon Redshift, Google BigQuery, and Snowflake.

Looker's documentation offers instructions on how to configure and connect your data warehouse. In most cases, it's simply a matter of creating and copying access credentials, which may include a username, password, and server information. You can then move data from your various data sources into your data warehouse for Looker to use.

Once your data warehouse is connected to Looker, you can build constructs known as explores, each of which is a SQL view containing a specific set of data for analysis. An example might be "orders" or "customers."

Once you've selected any given explore, you can filter data based on any column available in the view, group data based on certain fields in the view (known as dimensions), calculate outputs such as sums and counts (known as measures), and pick a visualization type such as a bar chart, pie chart, map, or bubble chart.

Beyond this simple use case, Looker offers a broad universe of functionality that allows you to conduct analyses and share them with your organization. You can get started with this walkthrough in Looker's documentation.

At this point you've coded up a script or written a program to get the data you want and successfully moved it into your data warehouse. But how will you load new or updated data? It's not a good idea to replicate all of your data each time you have updated records. That process would be painfully slow and resource-intensive.

Instead, identify key fields that your script can use to bookmark its progression through the data and use to pick up where it left off as it looks for updated data. Auto-incrementing fields such as updated_at or created_at work best for this. When you've built in this functionality, you can set up your script as a cron job or continuous loop to get new data as it appears in Square.

And remember, as with any code, once you write it, you have to maintain it. If Square modifies its API, or the API sends a field with a datatype your code doesn't recognize, you may have to modify the script. If your users want slightly different information, you definitely will have to.