Oracle优化器在处理伪列的时候是怎么做的？

sqysl

hi,yong huang:
      you are right,the plan indeed misled me.

Yong Huang

The first case shows FTS while the second (where you have rownum in the inline view) does not. The key is "STOPKEY" in the plan.

Actually, on second check in Jonathan's CBO book, he was talking about two cases that both have the same cost in the plans and yet the stats are different. That's a real case of a misleading plan, while here we can tell even by looking at the plan cost. I.e., checking stats simply confirms the plan cost.

Yong Huang

zhuojm

COUNT STOPKEY
意味着全表扫表的时候随时判断是否满足rownum的条件，只要满足马上停止．
COUNT
意味着把扫表的数据全部缓冲，并设置rownum，然后判断是否满足rownum的条件．

喝酒了，如果说错了原谅我．

foxmile

路过了解一下。