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# Client

## How to connect

You must specify PostgreSQL user and PostgreSQL database to connect
Apache Arrow Flight SQL endpoint.

User name and password must be passed by `Handshake` call. Note that
basic authentication is only supported for now. mTLS (mutual-TLS)
isn't implemented yet. If you're interested in mTLS, please see the
issue for it:
https://github.com/apache/arrow-flight-sql-postgresql/issues/79

You need to use a header to specify PostgreSQL database. The header
name for PostgreSQL database is `x-flight-sql-database`.

````{tab} Apache Arrow Flight SQL C++ client
You need to use
[`arrow::flight::FlightClient::AuthenticateBasicToken()`][arrow-flight-authenticate-basic]
for authentication.

You need to add a `x-flight-sql-database` header to
[`arrow::flight::FlightCallOptions::headers`][arrow-flight-call-options-headers]
for database.

The following example uses `PGUSER` (fallback to `USER`) and
`PGPASSWORD` environment variables like
`libpq`. `AuthenticateBasicToken()` returns Bearer token on
success. So the example users the returned Bearer token to request
headers to use following requests.

The following example uses `PGDATABASE` (fallback to `PGUSER`/`USER`)
environment variable like `libpq`.

```{literalinclude} ../../example/flight-sql/authenticate-password.cc
:language: c++
:linenos:
:tab-width: 4
:start-after: // Start authentication
:end-before: // End authentication
```
````

````{tab} ADBC Flight SQL driver
You need to set the
`username` and `password` options for authentication. See also the
[Authentication][arrow-adbc-authentication] document.

You need to set the
`adbc.flight.sql.rpc.call_header.x-flight-sql-database` option for
database. See also the [Custom Call
Headers][arrow-adbc-custom-call-headers] document.

```{literalinclude} ../../example/adbc/authenticate-password.c
:language: c
:linenos:
:tab-width: 4
:start-after: // Start authentication
:end-before: // End authentication
```
````

## How to query

You can use an ad-hoc SQL statement or a prepared SQL statement to
query.

### Ad-hoc SQL statement

````{tab} Apache Arrow Flight SQL C++ client

You need to use
[`arrow::flight::sql::FlightSqlClient::Execute()`][arrow-flight-sql-client-execute]
to execute a query.

You need to use
[`arrow::flight::sql::FlightSqlClient::DoGet()`][arrow-flight-sql-client-do-get]
to get results.

```{literalinclude} ../../example/flight-sql/query-ad-hoc.cc
:language: c++
:linenos:
:tab-width: 4
:start-after: // Start query
:end-before: // End query
```
````

```{tab} ADBC Flight SQL driver
TODO
```

### Prepared SQL statement

````{tab} Apache Arrow Flight SQL C++ client
You need to use
[`arrow::flight::sql::FlightSqlClient::Prepare()`][arrow-flight-sql-client-prepare]
to prepare a query.

You need to use
[`arrow::flight::sql::PreparedStatement::SetParameters()`][arrow-flight-sql-prepared-statement-set-parameters]
to set parameters.

You need to use
[`arrow::flight::sql::PreparedStatement::Execute()`][arrow-flight-sql-prepared-statement-execute]
to execute a prepared statement with parameters.

You need to use
[`arrow::flight::sql::FlightSqlClient::DoGet()`][arrow-flight-sql-client-do-get]
to get results.

```{literalinclude} ../../example/flight-sql/query-prepared.cc
:language: c++
:linenos:
:tab-width: 4
:start-after: // Start query
:end-before: // End query
```
````

```{tab} ADBC Flight SQL driver
TODO
```

[arrow-adbc-authentication]: https://arrow.apache.org/adbc/current/driver/flight_sql.html#authentication
[arrow-adbc-custom-call-headers]: https://arrow.apache.org/adbc/current/driver/flight_sql.html#custom-call-headers
[arrow-flight-authenticate-basic]: https://arrow.apache.org/docs/cpp/api/flight.html#clients
[arrow-flight-call-options-headers]: https://arrow.apache.org/docs/cpp/api/flight.html#_CPPv4N5arrow6flight17FlightCallOptions7headersE
[arrow-flight-sql-client-do-get]: https://arrow.apache.org/docs/cpp/api/flightsql.html#_CPPv4N5arrow6flight3sql15FlightSqlClient5DoGetERK17FlightCallOptionsRK6Ticket
[arrow-flight-sql-client-execute]: https://arrow.apache.org/docs/cpp/api/flightsql.html#_CPPv4N5arrow6flight3sql15FlightSqlClient7ExecuteERK17FlightCallOptionsRKNSt6stringERK11Transaction
[arrow-flight-sql-client-prepare]: https://arrow.apache.org/docs/cpp/api/flightsql.html#_CPPv4N5arrow6flight3sql15FlightSqlClient7PrepareERK17FlightCallOptionsRKNSt6stringERK11Transaction
[arrow-flight-sql-prepared-statement-execute]: https://arrow.apache.org/docs/cpp/api/flightsql.html#_CPPv4N5arrow6flight3sql17PreparedStatement7ExecuteERK17FlightCallOptions
[arrow-flight-sql-prepared-statement-set-parameters]: https://arrow.apache.org/docs/cpp/api/flightsql.html#_CPPv4N5arrow6flight3sql17PreparedStatement13SetParametersENSt10shared_ptrI11RecordBatchEE