Differences between char, varchar, varchar2, nvarchar, and nvarchar2

1. the char length is fixed, while the varchar2 length can be changed.
2. Char is more efficient than varchar2.

Comparison:
Varchar2 saves space than char, and is slightly less efficient than Char. That is, to achieve efficiency, a certain amount of space must be sacrificed, this is what we often say in database design, "Change space for efficiency '. Although varchar2 saves space than char, if a varchar2 column is often modified and the length of the data to be modified is different each time, this will cause row migration, this causes redundant I/O, which should be avoided during database design and adjustment. In this case, it would be better to replace varchar2 with Char.

The difference between varchar and varchar2 is that the latter occupies two bytes of all characters. The former only occupies two bytes of Chinese characters and full-angle characters.
The difference between nvarchar and nvarchar2 is the same as above. The difference is the type defined according to the Unicode standard. It is usually used to support the definition of a system similar to a multi-country language.