column_statistics Action

Implement the column_statistics DoAction to provide min/max values, distinct counts, and null statistics for query optimization.

The column_statistics action provides DuckDB with statistical information about a column in a table. These statistics enable the query optimizer to make better execution decisions, such as choosing optimal join strategies or filtering approaches. Implementing this action is optional and can be done selectively for specific tables.

Input Parameters

The action receives a single msgpack-serialized parameter:

struct GetFlightColumnStatistics
{
  std::string flight_descriptor;
  std::string column_name;
  std::string type;

  MSGPACK_DEFINE_MAP(flight_descriptor, column_name, type)
};

The flight_descriptor field is the Arrow Flight serialized FlightDescriptor structure.

The type field is the DuckDB data type name, i.e. VARCHAR, TIMESTAMP WITH TIME ZONE.

Return Value

The action must return an Arrow RecordBatch serialized using the IPC format with a single row containing the following fields:

Field Name	Type	Description
has_not_null	BOOLEAN	Indicate if the field contains a value that is not null.
has_null	BOOLEAN	Indicate if the field contains a value that is null.
distinct_count	UINT64	Indicate the number of distinct values in the field.
min	Depends on column type	The minimum value of the field.
max	Depends on column type	The maximum value of the field.
max_string_length	UINT64	The maximum length of a string value
contains_unicode	BOOLEAN	Indicate if the field contains Unicode text.