what is difference b/t varchar and nvarchar code example

Example 1: difference between varchar and nvarchar

Nvarchar stores UNICODE data. If you have requirements to store UNICODE or multilingual data, nvarchar is the choice. Varchar stores ASCII data and should be your data type of choice for normal use. Regarding memory usage, nvarchar uses 2 bytes per character, whereas varchar uses 1.

Example 2: difference between varchar and varchar2

Both VARCHAR & VARCHAR2 are Oracle 
data types that are used to store character
strings of variable length.

As I remember Varchar2 can store double of
Varchar datatype. Varchar2 also release
the unused characters. It is like Varchar2.0 :)