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 tampa_cv_pilot_signal_phasing_and_timing_spat table in this repository, by referencing it like:
"datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n:latest"."tampa_cv_pilot_signal_phasing_and_timing_spat"or in a full query, like:
SELECT
":id", -- Socrata column ID
"spat_intersections_3", -- General status of the controller(s). This field is based on the J2735 Standard.
"spat_intersections_2", -- Signal phase state mapping to the lanes it applies to, and point in time it will end. It may contain both active and future states. This field is based on the J2735 Standard.
"metadata_schemaversion", -- Version of the metadata schema.
"metadata_externalid", -- External ID
"metadata_rsuid", -- Identifier of road side unit.
"datatype", -- The data type.
"spat_timestamp", -- Timestamp of the Signal Phase and Timing (SPAT) message, expressed in minute of the year - the number of elapsed minutes of the current year in the time system being used (typically UTC time). This field is based on the J2735 Standard.
"metadata_generatedat", -- Closest time to which the record was created, either signed or received by the generatedBy source in UTC format. This information is taken from the communication header.
"spat_intersections_1", -- A sequence number within a stream of messages with the same DSRCmsgID and from the same sender. The receipt of a non-sequential MsgCount value (from the same sending device and message type) implies that one or more messages from that sending device may have been lost, unless MsgCount has been re-initialized due to an identity change. This field is based on the J2735 Standard.
"metadata_psid", -- Provider Service Identifier. A number that identifies a service provided by an application. PSID is defined in IEEE Std 1609.12.
"spat_intersections", -- SPAT intersection reference ID for a single intersection, consisting of a regionID and intersection ID assignment, and provides a unique mapping to the intersection MAP in question which provides complete location and approach/move/lane data. This field is based on the J2735 Standard.
"payload_data_spat_intersections_intersectionstate_regional", -- Regional Extension. This field is based on the J2735 Standard.
"payload_data_spat_intersections_intersectionstate_maneuverassis", -- Assist data consisting of a list of ConnectionManeuverAssist entries. This field is based on the J2735 Standard.
"spat_intersections_4", -- The mSec point in the current UTC minute that the message was constructed. This field is based on the J2735 Standard.
"payload_data_spat_regional", -- Regional Extension. This field is based on the J2735 Standard.
"randomnum", -- Random decimal number, to be used for random sampling of data within Socrata. This field is created for use within Socrata and is not present in the data Sandbox.
"metadata_kind", -- Metadata kind.
"payload_data_spat_intersections_intersectionstate_id_region", -- Road Regulator ID - a globally unique regional assignment value, typically assigned to a regional DOT authority. The value zero is used for testing. This field is based on the J2735 Standard.
"payload_data_spat_name", -- Human readable name for this collection of SPAT messages - to be used only in debug mode. This field is based on the J2735 Standard.
"metadata_generatedby", -- Source of the record, whether [OBU, RSU, TMC].
"payload_data_spat_intersections_intersectionstate_enabledlanes", -- Enabled lanes list - a list of lanes where the RevocableLane bit has been set which are now active and therefore part of the current intersection. Used for intersection at REL ramp. This field is based on the J2735 Standard.
"payload_data_spat_intersections_intersectionstate_moy", -- Minute of current UTC year, used only with messages to be archived. This field is based on the J2735 Standard.
"payload_data_spat_intersections_intersectionstate_name", -- Minute of current UTC year, used only with messages to be archived. This field is based on the J2735 Standard.
"metadata_logfilename" -- Name of the original file that deposited the message.
FROM
"datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n:latest"."tampa_cv_pilot_signal_phasing_and_timing_spat"
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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n 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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n: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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2nCheckout 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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n:latestThis will download all the objects for the latest tag of datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n 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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n: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 datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n: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, datahub-transportation-gov/tampa-cv-pilot-signal-phasing-and-timing-spat-xn7c-yu2n is just another Postgres schema.