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。