Oracle: 索引 与... where a = xx and b = xx and c = xx

chenjianjx

摘自《Troubleshooting Oracle Performance》


对于B-树索引

  如果在a,b,c三列分别建一个索引，则
     ... where a = xx and b = xx and c = xx 仍然非常低效


  如果在a,b,c三列上建立联合索引，则
       ... where a = xx and b = xx and c = xx 会高效的多
     而... where a = xx and b = xx  也会比较高效，即使c列没有出现在where子句

对于位图索引

  如果在a,b,c三列分别建一个索引，则
     ... where a = xx and b = xx and c = xx 已经可以达到高效