added type setter to column

src/sql/column.cpp

@@ -68,6 +68,11 @@ const std::string &column::ref_column() const
   return ref_column_;
 }
 
+void column::type(data_type_t type)
+{
+  type_ = type;
+}
+
 void column::alias(const std::string &as)
 {
   alias_ = as;