diff --git a/examples/example-multiple_datasets.cxx b/examples/example-multiple_datasets.cxx
new file mode 100644
index 0000000..30d552f
--- /dev/null
+++ b/examples/example-multiple_datasets.cxx
@@ -0,0 +1,42 @@
+#include <fstream>
+#include <sstream>
+#include <vector>
+
+#include "queryosity.h"
+#include "queryosity/hist.h"
+#include "queryosity/json.h"
+#include "queryosity/csv.h"
+
+using dataflow = qty::dataflow;
+namespace multithread = qty::multithread;
+namespace dataset = qty::dataset;
+namespace column = qty::column;
+namespace query = qty::query;
+
+using json = qty::json;
+using csv = qty::csv;
+using h1d = qty::hist::hist<double>;
+using linax = qty::hist::axis::regular;
+
+int main() {
+  dataflow df(multithread::enable(10));
+
+  std::ifstream data_json("data.json");
+  auto x = df.load(dataset::input<json>(data_json)).read(dataset::column<double>("x"));
+
+  std::ifstream data_csv("data.csv");
+  auto y = df.load(dataset::input<csv>(data_csv)).read(dataset::column<double>("y"));
+
+  auto z = x+y;
+
+  auto all = df.all();
+
+  auto h_z = df.make(query::plan<h1d>(linax(20,90.0,110.0)))
+                    .fill(z)
+                    .book(all)
+                    .result();
+
+  std::ostringstream os;
+  os << *h_z;
+  std::cout << os.str() << std::endl;
+}
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diff --git a/include/queryosity/column_series.h b/include/queryosity/column_series.h
new file mode 100644
index 0000000..444f1b3
--- /dev/null
+++ b/include/queryosity/column_series.h
@@ -0,0 +1,61 @@
+#pragma once
+
+#include "column.h"
+#include "dataflow.h"
+#include "lazy.h"
+#include "lazy_varied.h"
+#include "query_series.h"
+#include "selection.h"
+
+namespace queryosity {
+
+namespace column {
+
+/**
+ * @brief Argumnet for column series.
+ * @tparam Col (Varied) lazy column node.
+ * @todo C++20: Use concept to require lazy<column<Val>(::varied)>.
+ */
+template <typename Col> class series {
+
+public:
+  using value_type = column::value_t<typename Col::action_type>;
+
+public:
+  series(Col const &col);
+  ~series() = default;
+
+  auto _get(lazy<selection::node> &sel) const
+      -> lazy<query::series<value_type>>;
+
+  auto _get(lazy<selection::node>::varied &sel) const ->
+      typename lazy<query::series<value_type>>::varied;
+
+protected:
+  Col m_column;
+};
+
+} // namespace column
+
+} // namespace queryosity
+
+template <typename Col>
+queryosity::column::series<Col>::series(Col const &col) : m_column(col){};
+
+template <typename Col>
+auto queryosity::column::series<Col>::_get(lazy<selection::node> &sel) const
+    -> lazy<query::series<value_type>> {
+  auto df = sel.m_df;
+  return df->make(query::plan<query::series<value_type>>())
+      .fill(m_column)
+      .book(sel);
+}
+
+template <typename Col>
+auto queryosity::column::series<Col>::_get(lazy<selection::node>::varied &sel)
+    const -> typename lazy<query::series<value_type>>::varied {
+  auto df = sel.nominal().m_df;
+  return df->make(query::plan<query::series<value_type>>())
+      .fill(m_column)
+      .book(sel);
+}
\ No newline at end of file
diff --git a/include/queryosity/query_booker.h b/include/queryosity/query_booker.h
new file mode 100644
index 0000000..e8b7aaa
--- /dev/null
+++ b/include/queryosity/query_booker.h
@@ -0,0 +1,86 @@
+
+#pragma once
+
+#include <functional>
+#include <utility>
+#include <vector>
+
+#include "query.h"
+
+namespace queryosity {
+
+template <typename T> class query::booker {
+
+public:
+  using query_type = T;
+
+public:
+  template <typename... Args> booker(Args... args);
+  ~booker() = default;
+
+  // copyable
+  booker(const booker &) = default;
+  booker &operator=(const booker &) = default;
+
+  template <typename... Vals>
+  auto add_columns(column::valued<Vals> const &...cols) const
+      -> std::unique_ptr<booker<T>>;
+
+  auto set_selection(const selection::node &sel) const -> std::unique_ptr<T>;
+
+protected:
+  std::unique_ptr<T> make_query();
+  template <typename... Vals>
+  void fill_query(column::valued<Vals> const &...cols);
+
+protected:
+  std::function<std::unique_ptr<T>()> m_make_unique_query;
+  std::vector<std::function<void(T &)>> m_add_columns;
+};
+
+} // namespace queryosity
+
+template <typename T>
+template <typename... Args>
+queryosity::query::booker<T>::booker(Args... args)
+    : m_make_unique_query(std::bind(
+          [](Args... args) { return std::make_unique<T>(args...); }, args...)) {
+}
+
+template <typename T>
+template <typename... Vals>
+auto queryosity::query::booker<T>::add_columns(
+    column::valued<Vals> const &...columns) const -> std::unique_ptr<booker<T>> {
+  // use a fresh one with its current fills
+  auto filled = std::make_unique<booker<T>>(*this);
+  // add fills
+  filled->fill_query(columns...);
+  // return new book
+  return filled;
+}
+
+template <typename T>
+template <typename... Vals>
+void queryosity::query::booker<T>::fill_query(
+    column::valued<Vals> const &...columns) {
+  // use a snapshot of its current calls
+  m_add_columns.push_back(std::bind(
+      [](T &cnt, column::valued<Vals> const &...cols) {
+        cnt.enter_columns(cols...);
+      },
+      std::placeholders::_1, std::cref(columns)...));
+}
+
+template <typename T>
+auto queryosity::query::booker<T>::set_selection(const selection::node &sel) const
+    -> std::unique_ptr<T> {
+  // call constructor
+  auto cnt = m_make_unique_query();
+  // fill columns (if set)
+  for (const auto &fill_query : m_add_columns) {
+    fill_query(*cnt);
+  }
+  // book cnt at the selection
+  cnt->set_selection(sel);
+  return cnt;
+}
\ No newline at end of file