Creating tables using varchar2 datatype by default allocates specified value in bytes. That means if one is storing multi-byte character then you may not be able to store all the characters as some character might be multi-byte i.e taking 2 bytes per character.
We can store multibyte charater strings with specified number of characters using CHAR along with the varchar2 datatype. e.g
Create table lingual ( text varchar2(2o) CHAR);
this way you can store up to 40 bytes or 20 multibyte characters in column text.
To find out how many characters a column of a row has, use length() function. This will return the number of character, multibyte or single byte.
Use lengthb() to determine the number of bytes the column value contains.