alter table [tableName] enable row movement;
flashback table [tableName] to timestamp to_timestamp('2017-05-31 19:40:00','yyyy-mm-dd HH24:MI:SS');
alter table [tableName] enable row movement;
flashback table [tableName] to timestamp to_timestamp('2017-05-31 19:40:00','yyyy-mm-dd HH24:MI:SS');