RBO基于规则的优化器access paths优先级:
RBO Path 1: Single Row by Rowid
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
注意在不违反如上优先级的前提下，若有2个优化级一样的索引可用，则RBO会选择晚建的那个索引， 解决方法是重建你想要让RBO使用的那个索引，或者使用CBO........ :lol:
在Oracle 10g以后虽然RBO (optimizer_mode=RULE)仍可用，但是不受官方的支持认可。