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 whidbey_basin_ctd_casts table in this repository, by referencing it like:
"kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96:latest"."whidbey_basin_ctd_casts"or in a full query, like:
SELECT
":id", -- Socrata column ID
"chlorophyll_g_l", -- Chlorophyll (µg/L)
"sa_qual", -- sa_qual
"salinity_psu", -- Salinity (PSU)
"dn_qual", -- dn_qual
"data_row_id", -- This is an internal database identifier used to uniquely identify each observation of data.
"turbidity_field", -- Turbidity Field
"temperature_c", -- Temperature (°C)
"sigma_theta_density_kg_m3", -- Sigma-Theta Density (kg/m3)
"scan", -- An internal numbering system used to describe the scan.
"par_surface", -- PAR Surface
"nitrate_nitrite_mg_n_l", -- Nitrate + Nitrite (mg N/L)
"dissolved_oxygen_mg_l", -- Dissolved Oxygen (mg/L)
"sample_date", -- The date of the observation.
"do_qual", -- do_qual
"locator", -- Unique geographic identifier used by King County to describe the location of the sensor reading.
"lt_qual", -- Light Transmission Qualifier
"cast_notes", -- KCEL notes from the CTD cast
"pa_qual", -- pa_qual
"pas_qual", -- pas_qual
"loaddate", -- This field shows on what date the data was loaded into the CTD database. Occasionally, revisions occur and the load date is the column which signifies that data was later corrected.
"par_field", -- PAR field
"light_transmission", -- Light Transmission
"density_field", -- Density
"depth_meters", -- Sensor depth when measurement was taken.
"st_qual", -- st_qual
"up_down", -- Description of whether the sensor was on the down or up cast.
"no23_qual", -- no23_qual
"ch_qual", -- ch_qual
"tb_qual", -- tb_qual
"summ_row_id", -- An internal numbering system used to track related observations from a given sample day.
"sd_qual" -- sd_qual
FROM
"kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96:latest"."whidbey_basin_ctd_casts"
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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96 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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96: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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96Checkout 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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96:latestThis will download all the objects for the latest tag of kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96 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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96: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 kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96: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, kingcounty-gov/whidbey-basin-ctd-casts-uz4m-4d96 is just another Postgres schema.