added mysql backend

backends/sqlite/include/sqlite_connection.hpp

@@ -35,7 +35,7 @@ public:
 
   sql::record describe(const std::string& table) override;
 
-  bool exists(const std::string &table_name) override;
+  bool exists(const std::string &schema_name, const std::string &table_name) override;
 
 private:
   struct fetch_context

backends/sqlite/src/sqlite_connection.cpp

@@ -156,7 +156,6 @@ sql::record sqlite_connection::describe(const std::string& table)
     auto index = strtoul(reader.column(0), &end, 10);
     std::string name = reader.column(1);
 
-    // Todo: extract size
     auto type = (string2type(reader.column(2)));
     end = nullptr;
     utils::constraints options{};
@@ -170,7 +169,7 @@ sql::record sqlite_connection::describe(const std::string& table)
   return std::move(prototype);
 }
 
-bool sqlite_connection::exists(const std::string &table_name)
+bool sqlite_connection::exists(const std::string &schema_name, const std::string &table_name)
 {
   const auto result = fetch_internal("SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND tbl_name='" + table_name + "' LIMIT 1");
   sqlite_result_reader reader(result.rows, result.prototype.size());