diff --git a/.vscode/c_cpp_properties.json b/.vscode/c_cpp_properties.json
index 625067d..68f4084 100644
--- a/.vscode/c_cpp_properties.json
+++ b/.vscode/c_cpp_properties.json
@@ -10,13 +10,12 @@
             },
             "includePath": [
                 "${workspaceFolder}/**",
-                "${workspaceFolder}/stdlib",
                 "/usr/local/opt/openssl/include",
                 "${workspaceFolder}"
             ],
             "defines": [],
             "macFrameworkPath": [
-                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks"
+                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks"
             ],
             "compilerPath": "/usr/bin/clang",
             "cStandard": "c11",
diff --git a/Readme.md b/Readme.md
index 971ac34..4cfde06 100644
--- a/Readme.md
+++ b/Readme.md
@@ -1,3 +1,6 @@
+### WIP
+compare in row.cpp shoud take into account m_visible
+
 ### TODO
 - create local_install.sh
 
@@ -14,7 +17,6 @@
 	- add drop m_index
 - support for joining
 
-- use string_to_double and string_to_long (from Table) everywhere
 - add const wherever should be
 - use static methods where posible
 - use references where pointer cannot be nullptr
diff --git a/main.cpp b/main.cpp
index 36fa181..d09309c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -117,7 +117,7 @@ void repl() {
 				result->print();
 
 				code += input + "\n";
-			} catch (std::exception &e) {
+			} catch (const std::exception &e) {
 				std::cerr << e.what() << std::endl;
 			}
 		}
diff --git a/settings.cpp b/settings.cpp
index ca36be8..f884af9 100644
--- a/settings.cpp
+++ b/settings.cpp
@@ -19,7 +19,7 @@ std::vector<std::pair<std::string, std::string>> Settings::m_settings =
 long Settings::string_to_long(const std::string &intstr) {
 	try {
 		return std::stol(intstr);
-	} catch (std::invalid_argument &e) {
+	} catch (const std::invalid_argument &e) {
 		throw Exception("error parsing as integer: " + intstr);
 	}
 }
diff --git a/table.cpp b/table.cpp
index aa92412..f04e18b 100644
--- a/table.cpp
+++ b/table.cpp
@@ -183,7 +183,7 @@ void Table::commit_row(Row &row) {
 	try {
 		validate_row(row);
 		index_row(row);
-	} catch (Exception &e) {
+	} catch (const Exception &e) {
 		throw e;
 	}
 }
@@ -250,9 +250,9 @@ void Table::create_index(const Index& index) {
 
 bool Table::drop_index(const std::string &index_name) {
 	auto it = std::find_if(m_indexes.begin(), m_indexes.end(),
-						   [&index_name](const Index &idx) {
-							   return idx.get_index_name() == index_name;
-						   });
+				[&index_name](const Index &idx) {
+				return idx.get_index_name() == index_name;
+			});
 
 	if (it != m_indexes.end()) {
 		m_indexes.erase(it);
@@ -317,24 +317,25 @@ void Table::index_rows(const std::string &index_name) {
 
 Index * Table::get_index(const std::string &index_name) {
 	auto it = std::find_if(m_indexes.begin(), m_indexes.end(),
-						   [&index_name](const Index &idx) {
-							   return idx.get_index_name() == index_name;
-						   });
+				[&index_name](const Index &idx) {
+				return idx.get_index_name() == index_name;
+			});
 
 	return (it != m_indexes.end()) ? &(*it) : nullptr;
 }
 
 Index * Table::get_index_for_column(const std::string &col_name) {
 	auto it = std::find_if(m_indexes.begin(), m_indexes.end(),
-							[&col_name](const Index &idx) {
-								return idx.get_column_name() == col_name;
-							});
+				[&col_name](const Index &idx) {
+				return idx.get_column_name() == col_name;
+			});
 
 	return (it != m_indexes.end()) ? &(*it) : nullptr;
 }
 
-bool Table::empty() {
+bool Table::empty() const {
 	if (m_rows.empty())	return true;
+
 	for (const auto & r : m_rows)
 		if (r.is_visible()) return false;
 
diff --git a/table.h b/table.h
index 736de59..706558d 100644
--- a/table.h
+++ b/table.h
@@ -36,8 +36,8 @@ struct Table {
 
 	void print();
 
-	std::string				m_name;
-	std::vector<ColDefNode> m_col_defs;
+	std::string			m_name;
+	std::vector<ColDefNode>		m_col_defs;
 	std::vector<Row>		m_rows;
 	std::vector<Index>		m_indexes;
 
@@ -59,7 +59,7 @@ struct Table {
 	Index * get_index(const std::string &index_name);
 	Index * get_index_for_column(const std::string &col_name);
 
-	bool empty();
+	bool empty() const;
 
 	struct rows_scanner {
 		explicit rows_scanner(Table *tbl) : m_use_rowids(false), m_table(tbl), m_fscan_itr(tbl->m_rows.begin()) {}
@@ -72,7 +72,7 @@ struct Table {
 			Table *	m_table;
 			std::vector<Row>::iterator	m_fscan_itr;
 			std::vector<rowid_t>		m_rowids;
-			size_t						m_rowids_idx{};
+			size_t				m_rowids_idx{};
 	};
 
 };
diff --git a/usql.cpp b/usql.cpp
index dc901fe..3835007 100644
--- a/usql.cpp
+++ b/usql.cpp
@@ -11,7 +11,7 @@ std::unique_ptr<Table> USql::execute(const std::string &command) {
 		std::unique_ptr<Node> node = m_parser.parse(command);
 		return execute(*node);
 
-	} catch (std::exception &e) {
+	} catch (const std::exception &e) {
 		return create_stmt_result_table(-1, e.what(), 0);
 	}
 
diff --git a/usql.h b/usql.h
index 1e13978..17a9ee3 100644
--- a/usql.h
+++ b/usql.h
@@ -84,10 +84,10 @@ private:
     static std::unique_ptr<ValueNode> count_function(ColValue *agg_func_value, const std::vector<std::unique_ptr<ValueNode>> &evaluatedPars);
 
     static void select_row(SelectFromTableNode &where_node,
-						   Table *src_table, Row *src_row,
-						   Table *rslt_table,
-						   const std::vector<ColDefNode> &rslt_tbl_col_defs, const std::vector<int> &src_table_col_index,
-						   bool is_aggregated) ;
+						    Table *src_table, Row *src_row,
+						    Table *rslt_table,
+					        const std::vector<ColDefNode> &rslt_tbl_col_defs, const std::vector<int> &src_table_col_index,
+						    bool is_aggregated);
 
     std::pair<bool, std::vector<rowid_t>> probe_index_scan(const Node *where, Table *table) const;
 	std::pair<bool, std::vector<rowid_t>> look_for_usable_index(const Node *where, Table *table) const;
diff --git a/usql_dml.cpp b/usql_dml.cpp
index 0e810fe..791aad3 100644
--- a/usql_dml.cpp
+++ b/usql_dml.cpp
@@ -4,8 +4,9 @@
 
 #include <algorithm>
 
-namespace usql {
 
+namespace usql {
+	
 
 std::pair<bool, std::vector<rowid_t>> USql::probe_index_scan(const Node *where, Table *table) const {
 	bool indexscan_possible = normalize_where(where);
@@ -85,28 +86,28 @@ void USql::select_row(SelectFromTableNode &where_node,
 					  const std::vector<int> &src_table_col_index,
 					  bool is_aggregated) {
 
-	    Row *rslt_row = nullptr;
+	Row *rslt_row = nullptr;
 	    
         // when aggregate functions in rslt_table only one row exists
-		if (is_aggregated && !rslt_table->empty())
-			rslt_row = &rslt_table->m_rows[0];
-		else
-			rslt_row = &rslt_table->create_empty_row();
+	if (is_aggregated && !rslt_table->empty())
+		rslt_row = &rslt_table->m_rows[0];
+	else
+		rslt_row = &rslt_table->create_empty_row();
 
-		for (auto idx = 0; idx < rslt_table->columns_count(); idx++) {
-			auto src_table_col_idx = src_table_col_index[idx];
+	for (auto idx = 0; idx < rslt_table->columns_count(); idx++) {
+		auto src_table_col_idx = src_table_col_index[idx];
 
-			if (src_table_col_idx == FUNCTION_CALL) {
-				auto evaluated_value = eval_value_node(src_table, *src_row, where_node.cols_names->operator[](idx).value.get(),
-													   const_cast<ColDefNode *>(&rslt_tbl_col_defs[idx]), &rslt_row->operator[](idx));
-				ValueNode *col_value = evaluated_value.get();
+		if (src_table_col_idx == FUNCTION_CALL) {
+			auto evaluated_value = eval_value_node(src_table, *src_row, where_node.cols_names->operator[](idx).value.get(),
+													const_cast<ColDefNode *>(&rslt_tbl_col_defs[idx]), &rslt_row->operator[](idx));
+			ValueNode *col_value = evaluated_value.get();
 
-				rslt_row->setColumnValue((ColDefNode *) &rslt_tbl_col_defs[idx], col_value);
-			} else {
-				ColValue &col_value = src_row->operator[](src_table_col_idx);
-				rslt_row->setColumnValue((ColDefNode *) &rslt_tbl_col_defs[idx], col_value);
-			}
+			rslt_row->setColumnValue((ColDefNode *) &rslt_tbl_col_defs[idx], col_value);
+		} else {
+			ColValue &col_value = src_row->operator[](src_table_col_idx);
+			rslt_row->setColumnValue((ColDefNode *) &rslt_tbl_col_defs[idx], col_value);
 		}
+	}
 
         // for aggregate is validated more than needed
         rslt_table->commit_row(*rslt_row);
diff --git a/usql_function.cpp b/usql_function.cpp
index dba9ccc..deef75c 100644
--- a/usql_function.cpp
+++ b/usql_function.cpp
@@ -82,8 +82,7 @@ std::unique_ptr<ValueNode> USql::pp_function(const std::vector<std::unique_ptr<V
 	return std::make_unique<StringValueNode>(parsed_value->getStringValue());
 }
 
-std::unique_ptr<ValueNode>
-USql::max_function(const std::vector<std::unique_ptr<ValueNode>> &evaluatedPars, const ColDefNode *col_def_node, ColValue *agg_func_value) {
+std::unique_ptr<ValueNode> USql::max_function(const std::vector<std::unique_ptr<ValueNode>> &evaluatedPars, const ColDefNode *col_def_node, ColValue *agg_func_value) {
 	if (col_def_node->type == ColumnType::integer_type || col_def_node->type == ColumnType::date_type) {
 		if (!evaluatedPars[0]->isNull()) {
 			auto val = evaluatedPars[0]->getIntegerValue();