Order by kth column

dev/alias.h

@@ -7,7 +7,7 @@
 namespace sqlite_orm {
 
     /**
-     *  This is base class for every class which is used as a custom table alias.
+     *  This is base class for every class which is used as a custom table alias, column alias or expression alias.
      *  For more information please look through self_join.cpp example
      */
     struct alias_tag {};
@@ -16,7 +16,7 @@ namespace sqlite_orm {
 
         /**
          *  This is a common built-in class used for custom single character table aliases.
-         *  Also you can use language aliases `alias_a`, `alias_b` etc. instead
+         *  For convenience there exist type aliases `alias_a`, `alias_b`, ...
          */
         template<class T, char A>
         struct table_alias : alias_tag {
@@ -37,7 +37,7 @@ namespace sqlite_orm {
 
             column_type column;
 
-            alias_column_t(){};
+            alias_column_t() {}
 
             alias_column_t(column_type column_) : column(std::move(column_)) {}
         };
@@ -72,6 +72,17 @@ namespace sqlite_orm {
             expression_type expression;
         };
 
+        /**
+         *  This is a common built-in class used for custom single-character column aliases.
+         *  For convenience there exist type aliases `colalias_a`, `colalias_b`, ...
+         */
+        template<char A>
+        struct column_alias : alias_tag {
+            static std::string get() {
+                return std::string(1u, A);
+            }
+        };
+
         template<class T>
         struct alias_holder {
             using type = T;
@@ -151,4 +162,14 @@ namespace sqlite_orm {
     using alias_y = internal::table_alias<T, 'y'>;
     template<class T>
     using alias_z = internal::table_alias<T, 'z'>;
+
+    using colalias_a = internal::column_alias<'a'>;
+    using colalias_b = internal::column_alias<'b'>;
+    using colalias_c = internal::column_alias<'c'>;
+    using colalias_d = internal::column_alias<'d'>;
+    using colalias_e = internal::column_alias<'e'>;
+    using colalias_f = internal::column_alias<'f'>;
+    using colalias_g = internal::column_alias<'g'>;
+    using colalias_h = internal::column_alias<'h'>;
+    using colalias_i = internal::column_alias<'i'>;
 }

dev/ast_iterator.h

@@ -654,9 +654,23 @@ namespace sqlite_orm {
             }
         };
 
+        /**
+         *  Column alias or literal
+         */
         template<class T>
-        struct ast_iterator<order_by_t<T>, void> {
-            using node_type = order_by_t<T>;
+        struct ast_iterator<
+            T,
+            std::enable_if_t<polyfill::disjunction_v<polyfill::is_specialization_of<T, alias_holder>,
+                                                     polyfill::is_specialization_of<T, literal_holder>>>> {
+            using node_type = T;
+
+            template<class L>
+            void operator()(const node_type& /*node*/, const L& /*l*/) const {}
+        };
+
+        template<class E>
+        struct ast_iterator<order_by_t<E>, void> {
+            using node_type = order_by_t<E>;
 
             template<class L>
             void operator()(const node_type& node, const L& l) const {

dev/conditions.h

@@ -6,12 +6,16 @@
 #include <tuple>  //  std::tuple, std::tuple_size
 #include <sstream>  //  std::stringstream
 
+#include "cxx_polyfill.h"
+#include "type_traits.h"
 #include "collate_argument.h"
 #include "constraints.h"
 #include "optional_container.h"
 #include "serializer_context.h"
 #include "tags.h"
 #include "expression.h"
+#include "type_printer.h"
+#include "literal.h"
 
 namespace sqlite_orm {
 
@@ -1172,14 +1176,28 @@ namespace sqlite_orm {
     }
 
     /**
-     * ORDER BY column
-     * Example: storage.select(&User::name, order_by(&User::id))
+     * ORDER BY column, column alias or expression
+     * 
+     * Examples:
+     * storage.select(&User::name, order_by(&User::id))
+     * storage.select(as<colalias_a>(&User::name), order_by(get<colalias_a>()))
      */
-    template<class O>
+    template<class O, internal::satisfies_not<std::is_base_of, integer_printer, type_printer<O>> = true>
     internal::order_by_t<O> order_by(O o) {
         return {std::move(o)};
     }
 
+    /**
+     * ORDER BY positional ordinal
+     * 
+     * Examples:
+     * storage.select(&User::name, order_by(1))
+     */
+    template<class O, internal::satisfies<std::is_base_of, integer_printer, type_printer<O>> = true>
+    internal::order_by_t<internal::literal_holder<O>> order_by(O o) {
+        return {{std::move(o)}};
+    }
+
     /**
      * ORDER BY column1, column2
      * Example: storage.get_all<Singer>(multi_order_by(order_by(&Singer::name).asc(), order_by(&Singer::gender).desc())

dev/get_prepared_statement.h

@@ -123,9 +123,9 @@ namespace sqlite_orm {
     const auto& get(const internal::prepared_statement_t<T>& statement) {
         using statement_type = typename std::decay<decltype(statement)>::type;
         using expression_type = typename statement_type::expression_type;
-        using node_tuple = typename internal::node_tuple<expression_type>::type;
+        using node_tuple = internal::node_tuple_t<expression_type>;
         using bind_tuple = typename internal::bindable_filter<node_tuple>::type;
-        using result_tupe = typename std::tuple_element<static_cast<size_t>(N), bind_tuple>::type;
+        using result_tupe = std::tuple_element_t<static_cast<size_t>(N), bind_tuple>;
         const result_tupe* result = nullptr;
         auto index = -1;
         internal::iterate_ast(statement.expression, [&result, &index](auto& node) {
@@ -146,9 +146,9 @@ namespace sqlite_orm {
     auto& get(internal::prepared_statement_t<T>& statement) {
         using statement_type = typename std::decay<decltype(statement)>::type;
         using expression_type = typename statement_type::expression_type;
-        using node_tuple = typename internal::node_tuple<expression_type>::type;
+        using node_tuple = internal::node_tuple_t<expression_type>;
         using bind_tuple = typename internal::bindable_filter<node_tuple>::type;
-        using result_tupe = typename std::tuple_element<static_cast<size_t>(N), bind_tuple>::type;
+        using result_tupe = std::tuple_element_t<static_cast<size_t>(N), bind_tuple>;
         result_tupe* result = nullptr;
         auto index = -1;
         internal::iterate_ast(statement.expression, [&result, &index](auto& node) {

dev/literal.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <utility>  //  std::move
+
+namespace sqlite_orm {
+    namespace internal {
+
+        /* 
+         *  Protect an otherwise bindable element so that it is always serialized as a literal value.
+         */
+        template<class T>
+        struct literal_holder {
+            using type = T;
+
+            T value;
+        };
+
+    }
+}