added sql function and alias

include/matador/sql/dialect.hpp

@@ -10,6 +10,8 @@
 
 namespace matador::sql {
 
+class column;
+
 class dialect
 {
 public:
@@ -61,6 +63,7 @@ public:
 
   using token_to_string_map = std::unordered_map<token_t, std::string>;
   using data_type_to_string_map = std::unordered_map<data_type_t, std::string>;
+  using sql_func_to_string_map = std::unordered_map<sql_function_t, std::string>;
 
 public:
   dialect() = default;
@@ -79,7 +82,7 @@ public:
  * @param str The identifier string to be prepared
  * @return The prepared string
  */
-  std::string prepare_identifier(const std::string &str) const;
+  std::string prepare_identifier(const column &col) const;
 
   /**
    * Prepare string literal
@@ -196,6 +199,15 @@ private:
     {data_type_t::type_null, "NULL"},
     {data_type_t::type_unknown, "UNKNOWN"}
   };
+
+  sql_func_to_string_map sql_func_map_ {
+    {sql_function_t::NONE,  "NONE" },
+    {sql_function_t::COUNT, "COUNT" },
+    {sql_function_t::AVG,   "AVG" },
+    {sql_function_t::SUM,   "SUM" },
+    {sql_function_t::MIN,   "MIN" },
+    {sql_function_t::MAX,   "MAX" },
+  };
 };
 
 }