relational operators added

parser.cpp

@@ -170,7 +170,7 @@ std::unique_ptr<Node> Parser::parse_operand_node() {
         case TokenType::identifier:
             return std::make_unique<DatabaseValueNode>(tokenString);
         default: ;
-            // Throw exception
+            throw Exception("Unknown operand node");
     }
 }
 
@@ -179,9 +179,17 @@ RelationalOperatorType Parser::parse_operator() {
     switch (op.type) {
         case TokenType::equal:
             return RelationalOperatorType::equal;
+        case TokenType::not_equal:
+            return RelationalOperatorType::not_equal;
         case TokenType::greater:
             return RelationalOperatorType::greater;
+        case TokenType::greater_equal:
+            return RelationalOperatorType::greater_equal;
+        case TokenType::lesser:
+            return RelationalOperatorType::lesser;
+        case TokenType::lesser_equal:
+            return RelationalOperatorType::lesser_equal;
         default: ;
-            // Throw exception
+            throw Exception("Unknown relational operator");
     }
 }