simple distinct added

usql.cpp

@@ -190,15 +190,24 @@ std::unique_ptr<Table> USql::execute_select(SelectFromTableNode &node) {
 		}
 	}
 
-	// order by
+	execute_distinct(node, result.get());
+
 	execute_order_by(node, table, result.get());
 
-	// offset & limit
 	execute_offset_limit(node.offset_limit, result.get());
 
 	return std::move(result);
 }
 
+void USql::execute_distinct(SelectFromTableNode &node, Table *result) const {
+	if (!node.distinct) return;
+	
+	auto compare_rows = [](const Row &a, const Row &b) { return a.compare(b) >= 0; };
+	std::sort(result->m_rows.begin(), result->m_rows.end(), compare_rows);
+
+	result->m_rows.erase(std::unique(result->m_rows.begin(), result->m_rows.end()), result->m_rows.end());
+}
+
 void USql::execute_order_by(SelectFromTableNode &node, Table *table, Table *result) const {
 	if (node.order_by.size() == 0) return;