Query the Data Delivery Network

The easiest way to query any data on Splitgraph is via the "Data Delivery Network" (DDN). The DDN is a single endpoint that speaks the PostgreSQL wire protocol. Any Splitgraph user can connect to it at data.splitgraph.com:5432 and query any version of over 40,000 datasets that are hosted or proxied by Splitgraph.

For example, you can query the master_addresses_list table in this repository, by referencing it like:

"cambridgema-gov/master-addresses-list-vup6-kpwv:latest"."master_addresses_list"

or in a full query, like:

SELECT
    ":id", -- Socrata column ID
    "neighborhood", -- Neighborhood planning group
    "representation_district", -- State representative district
    "census_block_group_2010", -- Census block group demographic area from the 2010 US Census.
    "address_id", -- Unique address ID used for master address database and address point GIS layer. See the GIS data dictionary for more information: http://www.cambridgema.gov/GIS/gisdatadictionary/Address/ADDRESS_AddressPoints 
    "police_car_route", -- Police Car Routes are areas which patrol cars are dispatched.
    "police_business_district", -- Police Business Regions are used for response and reporting by Cambridge Public Safety
    "election_polling_address", -- Polling address for elections
    "type", -- Address type. (e.g., building, park, other)
    "police_sector", -- Police Sectors are areas which police cars are dispatched using the computer aided dispatch (CAD) software.
    "police_neighborhood", -- Police Neighborhood Regions are used for response and reporting by Cambridge Public Safety.
    "census_block_2010", -- Census block demographic area from the 2010 US Census.
    "senate_district", -- State senate district 
    "stname",
    "election_precinct", -- Precinct number for elections
    "census_block_id_2020", -- Unique ID for 2020 Census Blocks.
    "police_walking_route", -- Police Walking Routes are areas which officers are dispatched using the computer aided dispatch (CAD) software.
    "cad_reporting_district", -- Public safety computer aided dispatch reporting district
    "street_number",
    "full_addr", -- Full street number and name
    "census_block_id_2010", -- Unique ID for 2010 Census Blocks.
    "building_id", -- Unique building ID
    "maplot", -- Parcel ID
    "census_block_group_2020", -- Census block group demographic area from the 2020 US Census.
    "commercial_district", -- Cambridge’s compact geography and population density allows the City’s vibrant commercial districts to offer a healthy retail mix to serve residents and visitors.
    "street_sweeping_district", -- City of Cambridge Department of Public Works Street Sweeping District.
    "census_tract_2020", -- Census tract demographic area from the 2020 US Census.
    "zip_code", -- Address zip code
    "latitude",
    "census_block_2020", -- Census block demographic area from the 2020 US Census.
    "election_ward", -- Ward number for elections
    "census_tract_2010", -- Census tract demographic area from the 2010 US Census.
    "longitude"
FROM
    "cambridgema-gov/master-addresses-list-vup6-kpwv:latest"."master_addresses_list"
LIMIT 100;

Connecting to the DDN is easy. All you need is an existing SQL client that can connect to Postgres. As long as you have a SQL client ready, you'll be able to query cambridgema-gov/master-addresses-list-vup6-kpwv with SQL in under 60 seconds.

This repository is an "external" repository. That means it's hosted elsewhere, in this case at data.cambridgema.gov. When you querycambridgema-gov/master-addresses-list-vup6-kpwv:latest on the DDN, we "mount" the repository using the socrata mount handler. The mount handler proxies your SQL query to the upstream data source, translating it from SQL to the relevant language (in this case SoQL).

We also cache query responses on the DDN, but we run the DDN on multiple nodes so a CACHE_HIT is only guaranteed for subsequent queries that land on the same node.

Query Your Local Engine

bash -c "$(curl -sL https://github.com/splitgraph/splitgraph/releases/latest/download/install.sh)"

Splitgraph Cloud is built around Splitgraph Core (GitHub), which includes a local Splitgraph Engine packaged as a Docker image. Splitgraph Cloud is basically a scaled-up version of that local Engine. When you query the Data Delivery Network or the REST API, we mount the relevant datasets in an Engine on our servers and execute your query on it.

It's possible to run this engine locally. You'll need a Mac, Windows or Linux system to install sgr, and a Docker installation to run the engine. You don't need to know how to actually use Docker; sgrcan manage the image, container and volume for you.

There are a few ways to ingest data into the local engine.

For external repositories (like this repository), the Splitgraph Engine can "mount" upstream data sources by using sgr mount. This feature is built around Postgres Foreign Data Wrappers (FDW). You can write custom "mount handlers" for any upstream data source. For an example, we blogged about making a custom mount handler for HackerNews stories.

For hosted datasets, where the author has pushed Splitgraph Images to the repository, you can "clone" and/or "checkout" the data using sgr cloneand sgr checkout.

Mounting Data

This repository is an external repository. It's not hosted by Splitgraph. It is hosted by data.cambridgema.gov, and Splitgraph indexes it. This means it is not an actual Splitgraph image, so you cannot use sgr clone to get the data. Instead, you can use the socrata adapter with the sgr mount command. Then, if you want, you can import the data and turn it into a Splitgraph image that others can clone.

First, install Splitgraph if you haven't already.

Mount the table with sgr mount

sgr mount socrata \
  "cambridgema-gov/master-addresses-list-vup6-kpwv" \
  --handler-options '{
    "domain": "data.cambridgema.gov",
    "tables": {
        "master_addresses_list": "vup6-kpwv"
    }
}'

That's it! Now you can query the data in the mounted table like any other Postgres table.

Query the data with your existing tools

Once you've loaded the data into your local Splitgraph engine, you can query it with any of your existing tools. As far as they're concerned, cambridgema-gov/master-addresses-list-vup6-kpwv is just another Postgres schema.