读书笔记,数据库优化器对应路径等级

基于规则的优化器使用的执行路径与各个路径对应的等级：

　　RBO Path 1: Single Row by Rowid(等级最高)

　　RBO Path 2: Single Row by Cluster Join

　　RBO Path 3: Single Row by Hash Cluster Key with Unique or Primary Key

　　RBO Path 4: Single Row by Unique or Primary Key

　　RBO Path 5: Clustered Join

　　RBO Path 6: Hash Cluster Key

　　RBO Path 7: Indexed Cluster Key

　　RBO Path 8: Composite Index

　　RBO Path 9: Single-Column Indexes

　　RBO Path 10: Bounded Range Search on Indexed Columns

　　RBO Path 11: Unbounded Range Search on Indexed Columns

　　RBO Path 12: Sort Merge Join

　　RBO Path 13: MAX or MIN of Indexed Column

　　RBO Path 14: ORDER BY on Indexed Column

　　RBO Path 15: Full Table Scan(等级最低)

摘自 :

http://tech.it168.com/a2009/0423/273/000000273783.shtml