Index range scan is a common operation for accessing selective data. It can be
bounded (bounded on both sides) or unbounded (on one or both sides). Data is
returned in the ascending order of index columns. Multiple rows with identical values
are sorted (in ascending order) by the ROWIDs.

索引范围
1. 索引范围扫描可以是封闭或者不风不的
2. 数据是以按照索引列的升序排列的