Arrow Flight SQL is a protocol for interacting with SQL databases using the Arrow in-memory format and the :doc:`Flight RPC <./Flight>` framework.

Generally, a database will implement the RPC methods according to the specification, but does not need to implement a client-side driver. A database client can use the provided Flight SQL client to interact with any database that supports the necessary endpoints. Flight SQL clients wrap the underlying Flight client to provide methods for the new RPC methods described here.

Flight SQL reuses the predefined RPC methods in Arrow Flight, and provides various commands that pair those methods with request/response messages defined via Protobuf (see below).

Flight SQL provides a variety of commands to fetch catalog metadata about the database server.

All of these commands can be used with the GetFlightInfo and GetSchema RPC methods. The Protobuf request message should be packed into a google.protobuf.Any message, then serialized and packed as the cmd field in a CMD-type FlightDescriptor.

If the command is used with GetFlightInfo, the server will return a FlightInfo response. The client should then use the Ticket(s) in the FlightInfo with the DoGet RPC method to fetch a Arrow data containing the results of the command. In other words, SQL metadata is returned as Arrow data, just like query results themselves.

The Arrow schema returned by GetSchema or DoGet for a particular command is fixed according to the specification.

CommandGetCatalogs

List the catalogs available in the database. The definition varies by vendor.

CommandGetCrossReference

List the foreign key columns in a given table that reference columns in a given parent table.

CommandGetDbSchemas

List the schemas (note: a grouping of tables, not an Arrow schema) available in the database. The definition varies by vendor.

CommandGetExportedKeys

List foreign key columns that reference the primary key columns of a given table.

CommandGetImportedKeys

List foreign keys of a given table.

CommandGetPrimaryKeys

List the primary keys of a given table.

CommandGetSqlInfo

Fetch metadata about the database server and its supported SQL features.

CommandGetTables

List tables in the database.

CommandGetTableTypes

List table types in the database. The list of types varies by vendor.

Flight SQL also provides commands to execute SQL queries and manage prepared statements.

Many of these commands are also used with GetFlightInfo/GetSchema and work identically to the metadata methods above. Some of these commands can be used with the DoPut RPC method, but the command should still be encoded in the request FlightDescriptor in the same way.

Commands beginning with "Action" are instead used with the DoAction RPC method, in which case the command should be packed into a google.protobuf.Any message, then serialized and packed into the body of a Flight Action. Also, the action type should be set to the command name (i.e. for ActionClosePreparedStatementRequest, the type should be ClosePreparedStatement).

ActionClosePreparedStatementRequest

Close a previously created prepared statement.

ActionCreatePreparedStatementRequest

Create a new prepared statement for a SQL query.

CommandPreparedStatementQuery

Execute a previously created prepared statement and get the results.

When used with DoPut: binds parameter values to the prepared statement.

When used with GetFlightInfo: execute the prepared statement. The prepared statement can be reused after fetching results.

CommandPreparedStatementUpdate

Execute a previously created prepared statement that does not return results.

When used with DoPut: execute the query and return the number of affected rows. The prepared statement can be reused afterwards.

CommandStatementQuery

Execute an ad-hoc SQL query.

When used with GetFlightInfo: execute the query (call DoGet to fetch results).

When used with GetSchema: return the schema of the query results.

CommandStatementUpdate

Execute an ad-hoc SQL query that does not return results.

When used with DoPut: execute the query and return the number of affected rows.

Listing available tables.

Executing an ad-hoc query.

Creating a prepared statement, then executing it.

• Introducing Apache Arrow Flight SQL: Accelerating Database Access

.. literalinclude:: ../../../format/FlightSql.proto
   :language: protobuf
   :linenos: