Query the Data Delivery Network
Query the DDNThe 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 richmond_county_current_data table in this repository, by referencing it like:
"novascotia-ca/richmond-county-current-data-d5cn-i8sx:latest"."richmond_county_current_data"or in a full query, like:
SELECT
":id", -- Socrata column ID
"sea_water_to_direction_degree", -- direction of water flow for corresponding depth bin and timestamp (degrees). Measured travelling away from the ADCP sensor relative to True North (a reading of 90 degrees describes current travelling from west to east).
"sea_water_speed_m_s", -- water speed for corresponding depth bin and timestamp (m / s).
"bin_depth_below_surface_m", -- distance from the surface to the centre of the measurement bin (metres). Calculated as sensor_depth_below_surface_m + sensor_height_above_sea_floor_m - bin_height_above_sea_floor_m. See “Nova Scotia Current Data: Deployment Information” dataset (https://data.novascotia.ca/d/rs2e-ekha) for sensor_height_above_sea_floor_m.
"bin_height_above_sea_floor_m", -- distance from the seafloor to the centre of the measurement bin (metres).
"datetime", -- timestamp of the start of the ensemble (in UTC). Current speed and direction recorded at each timestamp are an average of many measurements recoded during the ensemble. See the “Nova Scotia Current Data Deployment Information” dataset for ensemble details for each deployment.
"waterbody", -- waterbody in which the ADCP was deployed.
"deployment_id", -- unique identifier for ADCP deployment. IDs are assigned incrementally by deployment date within a county. A skipped ID (e.g., consecutive IDs are XY001 and XY003) indicates that an ADCP was deployed but no useable current data were recovered (e.g., the battery failed).
"sensor_depth_below_surface_m", -- the depth of the ADCP below the surface (metres), measured by the ADCP sensor. Changes with the tide.
"station" -- specific area where ADCP was deployed.
FROM
"novascotia-ca/richmond-county-current-data-d5cn-i8sx:latest"."richmond_county_current_data"
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 novascotia-ca/richmond-county-current-data-d5cn-i8sx with SQL in under 60 seconds.
Query Your Local Engine
bash -c "$(curl -sL https://github.com/splitgraph/splitgraph/releases/latest/download/install.sh)"Read the installation docs.
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, 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 (like this repository), where the author has pushed Splitgraph Images to the repository, you can "clone" and/or "checkout" the data using sgr cloneand sgr checkout.
Cloning Data
Because novascotia-ca/richmond-county-current-data-d5cn-i8sx:latest is a Splitgraph Image, you can clone the data from Spltgraph Cloud to your local engine, where you can query it like any other Postgres database, using any of your existing tools.
First, install Splitgraph if you haven't already.
Clone the metadata with sgr clone
This will be quick, and does not download the actual data.
sgr clone novascotia-ca/richmond-county-current-data-d5cn-i8sxCheckout the data
Once you've cloned the data, you need to "checkout" the tag that you want. For example, to checkout the latest tag:
sgr checkout novascotia-ca/richmond-county-current-data-d5cn-i8sx:latestThis will download all the objects for the latest tag of novascotia-ca/richmond-county-current-data-d5cn-i8sx and load them into the Splitgraph Engine. Depending on your connection speed and the size of the data, you will need to wait for the checkout to complete. Once it's complete, you will be able to query the data like you would any other Postgres database.
Alternatively, use "layered checkout" to avoid downloading all the data
The data in novascotia-ca/richmond-county-current-data-d5cn-i8sx:latest is 0 bytes. If this is too big to download all at once, or perhaps you only need to query a subset of it, you can use a layered checkout.:
sgr checkout --layered novascotia-ca/richmond-county-current-data-d5cn-i8sx:latestThis will not download all the data, but it will create a schema comprised of foreign tables, that you can query as you would any other data. Splitgraph will lazily download the required objects as you query the data. In some cases, this might be faster or more efficient than a regular checkout.
Read the layered querying documentation to learn about when and why you might want to use layered queries.
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, novascotia-ca/richmond-county-current-data-d5cn-i8sx is just another Postgres schema.