rounded card notes from AskTom

Note 1:What is a rounded cardinality?

rounded card是执行计划时的预测数值

original card是对象实际的原始的数值

Note 2: auto trace和explain plan有哪些区别：

  a) explain plan does not bind variable peek, a real query would.

b) explain plan sees all binds as varchar2's - in real life they are numbers, dates, varchar2's and 
so on.  Hence, implicit conversions may or may not be observed by explain plan that would be 
observed in real life.
c) explain plan does a hard parse, uses the statistics/dynamic samples that are IN PLACE RIGHT NOW. 
 A query that was run for real "a little while ago" or "a little while from now" might see 
different inputs
d) explain plan uses the current operational environment to come up with a plan.  You might be 
explaining in a FIRST_ROWS session, whereas the query was actually executed in a ALL_ROWS session 
(or any one of the optimizer parameters could be different)
e) any combination of a, b, c, d...

http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:63445044804318