When a column is of type char, the memory used will not be dependent on the value. It entirely depends on the bytes defined.
Example:
Name CHAR(10)
Each value will occupy 10 bytes of memory space even though the value may be of a smaller size.
When a column is of type varchar2, the memory used entirely depends on the value of the column
Example:
Name VARCHAR2(10)
Each value will occupy “x” bytes of memory space depending on the value.
To summarize, a char data type is usually used when the value of fixed size is ascertained; for example Student id.
On the other hand, varchar2 should be used for a variable length of data; for example, Name.
