added mysql backend

backends/postgres/include/postgres_connection.hpp

@@ -35,7 +35,7 @@ public:
 
   sql::record describe(const std::string& table) override;
 
-  bool exists(const std::string &table_name) override;
+  bool exists(const std::string &schema_name, const std::string &table_name) override;
 
 private:
   [[nodiscard]] static std::string generate_statement_name(const sql::query_context &query) ;

backends/postgres/include/postgres_statement.hpp

@@ -12,7 +12,7 @@ namespace matador::backends::postgres {
 class postgres_statement final : public sql::statement_impl
 {
 public:
-  postgres_statement(PGconn *db, PGresult *result, const std::string &name, const sql::query_context &query);
+  postgres_statement(PGconn *db, PGresult *result, std::string name, const sql::query_context &query);
 
   size_t execute() override;
   std::unique_ptr<sql::query_result_impl> fetch() override;