basic version of coalesce function

usql.cpp

@@ -173,6 +173,9 @@ std::unique_ptr<ValueNode> USql::eval_function_value_node(Table *table, Row &row
 		evaluatedPars.push_back(eval_value_node(table, row, param.get(), nullptr, nullptr));
 	}
 
+	// coalesce function can have first parameter null, so must be calles before following "return null"
+	if (fnc->function == FunctionNode::Type::coalesce) return coalesce_function(evaluatedPars);
+	
 	if (evaluatedPars.empty() || evaluatedPars[0]->isNull())
 		return std::make_unique<NullValueNode>();