implemented sqlite fetch

src/sql/record.cpp

@@ -15,7 +15,7 @@ const column &record::at(const std::string &name) const
   return columns_by_name_.at(name).first;
 }
 
-const column &record::at(size_t index)
+const column &record::at(size_t index) const
 {
   return columns_.at(index);
 }
@@ -72,4 +72,15 @@ size_t record::size() const
   return columns_.size();
 }
 
-}
+bool record::empty() const
+{
+  return columns_.empty();
+}
+
+void record::clear()
+{
+  columns_.clear();
+  columns_by_name_.clear();
+}
+
+}