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 halifax_county_water_quality_data table in this repository, by referencing it like:
"novascotia-ca/halifax-county-water-quality-data-x9dy-aai9:latest"."halifax_county_water_quality_data"or in a full query, like:
SELECT
":id", -- Socrata column ID
"qc_flag_temperature_degree_c", -- Quality control flag for temperature. Maximum flag value from three automated quality control tests: grossrange, spike, and rolling_sd. Flag values can be: "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail"
"qc_flag_dissolved_oxygen_percent_saturation", -- Quality control flag for dissolved oxygen (percent saturation). Maximum flag value from four automated quality control tests: grossrange, climatology, spike, and rolling_sd. Flag values can be: "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail"
"sensor_depth_measured_m", -- Depth of the sensor, as measured by the sensor in metres
"dissolved_oxygen_percent_saturation", -- Dissolved oxygen measurement, in units of percent saturation
"depth_crosscheck_flag", -- Quality control flag for sensor depth at low tide. Flag values can be "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail". The same flag is applied to the whole deployment.
"sensor_depth_at_low_tide_m", -- Estimated depth of the sensor at low tide, in metres, based on its position in the sensor string configuration
"timestamp_utc", -- Timestamp at which a measurement was made, in UTC. The formatting is "YYYY-MM-DD HH:MM:SS"
"sensor_serial_number", -- Unique identifying number for the sensor that recorded the measurement
"string_configuration", -- Configuration in which the sensors were deployed. This can be one of six entries: “sub-surface buoy”, “surface buoy”, “attached to gear”, “attached to fixed structure”, “floating dock”, or “unknown”
"deployment_range", -- String describing the instrument deployment and retrieval dates. The format is "YYYY-MMM-DD to YYYY-MMM-DD"
"longitude", -- Longitude of the deployment (decimal degrees)
"latitude", -- Latitude of the deployment (decimal degrees)
"station", -- Name of the location for this deployment
"waterbody", -- Waterbody in which the station for this deployment is located
"qc_flag_sensor_depth_measured_m", -- Quality control flag for measured sensor depth. Maximum flag value from three automated quality control tests: grossrange, spike, and rolling_sd. Flag values can be: "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail"
"qc_flag_salinity_psu", -- Quality control flag for salinity. Maximum flag value from three automated quality control tests: grossrange, spike, and rolling_sd. Flag values can be: "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail"
"qc_flag_dissolved_oxygen_uncorrected_mg_per_l", -- Quality control flag for dissolved oxygen (mg/L). Maximum flag value from four automated quality control tests: grossrange, climatology, spike, and rolling_sd. Flag values can be: "Pass", "Not Evaluated", "Suspect/Of Interest", or "Fail"
"lease", -- Aquaculture lease number associated with the station (where applicable)
"temperature_degree_c", -- Temperature measurement, in degrees Celsius
"salinity_psu", -- Salinity measurement, in practical salinity units
"dissolved_oxygen_uncorrected_mg_per_l", -- Dissolved oxygen measurement, in units of mg/L, without applying a salinity correction factor
"sensor_type" -- Model of the sensor that recorded the measurement
FROM
"novascotia-ca/halifax-county-water-quality-data-x9dy-aai9:latest"."halifax_county_water_quality_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/halifax-county-water-quality-data-x9dy-aai9 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/halifax-county-water-quality-data-x9dy-aai9: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/halifax-county-water-quality-data-x9dy-aai9Checkout 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/halifax-county-water-quality-data-x9dy-aai9:latestThis will download all the objects for the latest tag of novascotia-ca/halifax-county-water-quality-data-x9dy-aai9 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/halifax-county-water-quality-data-x9dy-aai9: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/halifax-county-water-quality-data-x9dy-aai9: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/halifax-county-water-quality-data-x9dy-aai9 is just another Postgres schema.