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