langchain/document_loaders/duckdb_loader.py/DuckDBLoader/load
class DuckDBLoader:    def load(self) -> List[Document]:
        try:
            import duckdb
        except ImportError:
            raise ImportError(
                "Could not import duckdb python package. "
                "Please install it with `pip install duckdb`."
            )

        docs = []
        with duckdb.connect(
            database=self.database, read_only=self.read_only, config=self.config
        ) as con:
            query_result = con.execute(self.query)
            results = query_result.fetchall()
            description = cast(list, query_result.description)
            field_names = [c[0] for c in description]

            if self.page_content_columns is None:
                page_content_columns = field_names
            else:
                page_content_columns = self.page_content_columns

            if self.metadata_columns is None:
                metadata_columns = []
            else:
                metadata_columns = self.metadata_columns

            for result in results:
                page_content = "\n".join(
                    f"{column}: {result[field_names.index(column)]}"
                    for column in page_content_columns
                )

                metadata = {
                    column: result[field_names.index(column)]
                    for column in metadata_columns
                }

                doc = Document(page_content=page_content, metadata=metadata)
                docs.append(doc)

        return docs