distintas ordenes LENGH en oracle

Syntax

length::=

Purpose

The LENGTH functions return the length of char.  

LENGTH calculates length using characters as defined by the input character set.  
LENGTHB uses bytes instead of characters.  
LENGTHC uses Unicode complete characters.  
LENGTH2 uses UCS2 code points.  
LENGTH4 uses UCS4 code points.

 
char can be any of the datatypes CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. The return value is of datatype NUMBER. If char has datatype CHAR, then the length includes all trailing blanks. If char is null, then this function returns null.
Restriction on LENGTHB The LENGTHB function is supported for single-byte LOBs only. It cannot be used with CLOB and NCLOB data in a multibyte character set.

Examples

The following example uses the LENGTH function using a single-byte database character set:

SELECT LENGTH('CANDIDE') "Length in characters"
   FROM DUAL;

Length in characters
--------------------
                   7

The next example assumes a double-byte database character set.

SELECT LENGTHB ('CANDIDE') "Length in bytes"
   FROM DUAL;
 
Length in bytes
---------------
             14

Fuentes: http://docs.oracle.com/cd/B19306_01/server.102/b14200/img/length.gif 

http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions076.htm