diff --git a/include/matador/query/criteria/abstract_column_criteria.hpp b/include/matador/query/criteria/abstract_column_criteria.hpp
index 1947f5c..bf14770 100644
--- a/include/matador/query/criteria/abstract_column_criteria.hpp
+++ b/include/matador/query/criteria/abstract_column_criteria.hpp
@@ -15,7 +15,7 @@ public:
     [[nodiscard]] const table_column& col() const;
 
 protected:
-    table_column column_;
+    const table_column& column_;
 };
 
 }
diff --git a/include/matador/query/criteria/binary_criteria.hpp b/include/matador/query/criteria/binary_criteria.hpp
index 4fe28ea..61c4482 100644
--- a/include/matador/query/criteria/binary_criteria.hpp
+++ b/include/matador/query/criteria/binary_criteria.hpp
@@ -34,7 +34,7 @@ private:
 class binary_column_criteria final : public abstract_criteria {
 public:
     binary_column_criteria() = delete;
-    binary_column_criteria(table_column  left_column, binary_operator operand, table_column  right_column);
+    binary_column_criteria(const table_column& left_column, binary_operator operand, const table_column& right_column);
 
     void accept(criteria_visitor& visitor) const override;
 
@@ -43,9 +43,9 @@ public:
     [[nodiscard]] const table_column& right_column() const;
 
 private:
-    table_column left_column_;
+    const table_column& left_column_;
     binary_operator operator_{};
-    table_column right_column_;
+    const table_column& right_column_;
 };
 }
 #endif //CRITERIA_BINARY_CRITERIA_NODE_HPP
\ No newline at end of file
diff --git a/include/matador/query/expression/table_column_expression.hpp b/include/matador/query/expression/table_column_expression.hpp
index 2155965..26bdf60 100644
--- a/include/matador/query/expression/table_column_expression.hpp
+++ b/include/matador/query/expression/table_column_expression.hpp
@@ -8,14 +8,14 @@ namespace matador::query {
 class table_column_expression : public abstract_column_expression {
 public:
   table_column_expression() = delete;
-  explicit table_column_expression(table_column col);
+  explicit table_column_expression(const table_column& col);
 
   void accept(expression_visitor& visitor) const override;
 
   [[nodiscard]] const table_column& col() const;
 
 private:
-  table_column column_;
+  const table_column& column_;
 };
 }
 #endif //MATADOR_TABLE_COLUMN_EXPRESSION_HPP
\ No newline at end of file
diff --git a/source/orm/query/criteria/binary_criteria.cpp b/source/orm/query/criteria/binary_criteria.cpp
index 4014d7e..d8bcc18 100644
--- a/source/orm/query/criteria/binary_criteria.cpp
+++ b/source/orm/query/criteria/binary_criteria.cpp
@@ -25,7 +25,7 @@ const criteria_value& binary_criteria::value() const {
   return value_;
 }
 
-binary_column_criteria::binary_column_criteria(table_column  left_column, const binary_operator operand, table_column  right_column)
+binary_column_criteria::binary_column_criteria(const table_column& left_column, const binary_operator operand, const table_column& right_column)
 : left_column_(std::move(left_column))
 , operator_(operand)
 , right_column_(std::move(right_column)){}
diff --git a/source/orm/query/expression/table_column_expression.cpp b/source/orm/query/expression/table_column_expression.cpp
index 6f8a29c..efb8fcc 100644
--- a/source/orm/query/expression/table_column_expression.cpp
+++ b/source/orm/query/expression/table_column_expression.cpp
@@ -2,8 +2,8 @@
 #include "matador/query/expression/expression_visitor.hpp"
 
 namespace matador::query {
-table_column_expression::table_column_expression(table_column col)
-: column_(std::move(col)){
+table_column_expression::table_column_expression(const table_column& col)
+: column_(col){
 }
 
 void table_column_expression::accept(expression_visitor &visitor) const {
diff --git a/source/orm/query/expression_evaluator.cpp b/source/orm/query/expression_evaluator.cpp
index 781d2c6..646f0ea 100644
--- a/source/orm/query/expression_evaluator.cpp
+++ b/source/orm/query/expression_evaluator.cpp
@@ -50,7 +50,7 @@ void expression_evaluator::visit(const value_expression& node) {
   expression_.append(v.result);
 }
 
-void expression_evaluator::visit(const placeholder_expression& node) {
+void expression_evaluator::visit(const placeholder_expression& /*node*/) {
   query_.bind_vars.emplace_back(std::string("value_") + std::to_string(query_.bind_vars.size() + 1));
   expression_.append(dialect_.next_placeholder(query_.bind_vars));
 }