Method resultForMax1RowIter

pgserver/duck_handler.go:700–724

resultForMax1RowIter ensures that an empty iterator returns at most one row

(ctx *sql.Context, schema sql.Schema, iter sql.RowIter, resultFields []pgproto3.FieldDescription)

// resultForMax1RowIter ensures that an empty iterator returns at most one row
func (h *DuckHandler) resultForMax1RowIter(ctx *sql.Context, schema sql.Schema, iter sql.RowIter, resultFields []pgproto3.FieldDescription) (*Result, error) {
	defer trace.StartRegion(ctx, "DuckHandler.resultForMax1RowIter").End()
	row, err := iter.Next(ctx)
	if err == io.EOF {
		return &Result{Fields: resultFields}, nil
	} else if err != nil {
		return nil, err
	}

	if _, err = iter.Next(ctx); err != io.EOF {
		return nil, fmt.Errorf("result max1Row iterator returned more than one row")
	}
	if err := iter.Close(ctx); err != nil {
		return nil, err
	}

	outputRow, err := h.rowToBytes(ctx, schema, resultFields, row)
	if err != nil {
		return nil, err
	}

	ctx.GetLogger().Tracef("spooling result row %s", outputRow)

	return &Result{Fields: resultFields, Rows: []Row{{outputRow}}, RowsAffected: 1}, nil
}

// resultForDefaultIter reads batches of rows from the iterator
// and writes results into the callback function.