Byte (byte) is a unit of measurement computer system used to measure the storage capacity, the most commonly used is an 8-bit bytes, i.e., a byte contains 8 bits (bit) binary number
Is the length of a computer word processing data, depending on the cpu, usually 1 or more, generally speaking, the larger computer bits, the more data in the one-time processing on behalf of the computer
After a length of 5.0 mysql refers character length rather than byte length, i.e. varchar (100) can store 100 100 English characters or Chinese characters, in accordance with previous mysql 5.0 UTF-8 encoding transducer varchar (100) only You can store 100/3 characters, a kanji character, 3 bytes
the oracle VARCHAR2 (20) can store 10 characters