why length(date),vsize(date) returning different values?
Because they accept different parameter types and have different functionality. For their description, please consult SQL Language Referennce Guide for your Oracle version. It is available with other Oracle documentation books e.g. online on http://tahiti.oracle.com/
Originally Posted by vithalreddy
how the date is storing internally?
Use DUMP function. It is also described in SQL Language Reference. Anyway, it will be useless as you will not be able to enter it (yes, there is one way, but if you do not know about it, you definitely do not need it).