Description
Hello
I try to work with scalar data by analogy with the ClickHouse repository. To do this, I made a patch in which I supplemented the list of package types from the client with the value ClientCodes::Scalar. The number of this value is the same as the ServerCodes::Totals, as it was in the ClickHouse repository.
/// Types of packets received from server
namespace ServerCodes {
enum {
Hello = 0, /// Name, version, revision.
Data = 1, /// `Block` of data, may be compressed.
Exception = 2, /// Exception that occurred on server side during query execution.
Progress = 3, /// Query execcution progress: rows and bytes read.
Pong = 4, /// response to Ping sent by client.
EndOfStream = 5, /// All packets were sent.
ProfileInfo = 6, /// Profiling data
Totals = 7, /// Block of totals, may be compressed.
Extremes = 8, /// Block of mins and maxs, may be compressed.
TablesStatusResponse = 9, /// Response to TableStatus.
Log = 10, /// Query execution log.
TableColumns = 11, /// Columns' description for default values calculation
PartUUIDs = 12, /// List of unique parts ids.
ReadTaskRequest = 13, /// String (UUID) describes a request for which next task is needed
/// This is such an inverted logic, where server sends requests
/// And client returns back response
ProfileEvents = 14, /// Packet with profile events from server.
};
}
/// Types of packets sent by client.
namespace ClientCodes {
enum {
Hello = 0, /// Name, version, default database name.
Query = 1, /** Query id, query settings, query processing stage,
* compression status, and query text (no INSERT data).
*/
Data = 2, /// Data `Block` (e.g. INSERT data), may be compressed.
Cancel = 3, /// Cancel query.
Ping = 4, /// Check server connection.
Scalar = 7, /// Work with Block as scalar. NEW VALUE IS SAME ServerCodes::Totals
};
}I also added a bool is_scalar parameter to the Client::Impl::SendData to determine the type of record: scalar or data
void Client::Impl::SendData(const Block& block, const std::string& table_name, const bool is_scalar) {
if (is_scalar) {
WireFormat::WriteUInt64(*output_, ClientCodes::Scalar);
} else {
WireFormat::WriteUInt64(*output_, ClientCodes::Data);
}
if (server_info_.revision >= DBMS_MIN_REVISION_WITH_TEMPORARY_TABLES) {
WireFormat::WriteString(*output_, table_name);
}
if (compression_ == CompressionState::Enable) {
std::unique_ptr<OutputStream> compressed_output = std::make_unique<CompressedOutput>(output_.get(), options_.max_compression_chunk_size, options_.compression_method);
BufferedOutput buffered(std::move(compressed_output), options_.max_compression_chunk_size);
WriteBlock(block, buffered);
} else {
WriteBlock(block, *output_);
}
output_->Flush();
}and added const std::map<std::string, Block>& blocks to the Client::Execute for working with temp tables and scalars
void Client::Execute(const Query& query, const std::map<std::string, Block>& blocks, const bool is_scalar) {
impl_->ExecuteQuery(query, blocks, is_scalar);
}Here is an example of using working with a scalar
int main() {
Block answer;
auto handler = [&answer](const Block& block){
if( block.GetColumnCount() > 0 && block.GetRowCount() > 0 )
answer = block;
};
Query query( "SELECT $1 AS test"s );
query.OnData( handler );
auto value = std::make_shared< ColumnFloat64 >();
value->Append(3.14);
Block block;
block.AppendColumn("column"s, value);
map<string, Block> blocks { {""s, block} };
Client client( ClientOptions().SetHost( "localhost" ) );
client.Execute( query, blocks, true );
cout << answer[0]->AsStrict<ColumnFloat64>()->At(0) << endl;
return 0;
}As a result of executing this query, I expect a block with a single Float64 value, but when running this example, an exception is thrown with the text DB::Exception: Unknown expression identifier '$1' in scope SELECT '$1' AS test. Tell me please how to work with scalar?