The optimization of query sentences is to select operation sequence with minimal costs in terms of given query so as to make query a time-saving and space-saving process.
查询语句的优化就是对于给定的查询，选择代价最小的操作序列，使查询过程既节省时间，又节省空间。
2
More than 50 years later, director Steven Spielberg4 would go to great lengths to reproduce the look of that "error" for his harrowing D-Day landing sequence in Saving Private Ryan.