字符长度：oracle length(),mysql char_length(),sqlserver len()
字节长度：oracle lengthb(),mysql length(),sqlserver datalength()

mssql len datalength
LEN:返回指定字符串表达式的字符（而不是字节）数，其中不包含尾随空格。
DATALENGTH:返回用于表示任何表达式的字节数。
http://www.cnblogs.com/supperwu/archive/2011/11/22/2258469.html
http://www.cnblogs.com/supperwu/archive/2011/11/22/2258469.html

oracle:length lengthb
The LENGTH functionsreturn the length of char. LENGTH calculates length usingcharacters as defined by the input character set.
     --返回以字符为单位的长度.

LENGTHB usesbytes instead of characters.
     --返回以字节为单位的长度.

LENGTHC usesUnicode complete characters.
     --返回以Unicode完全字符为单位的长度.

LENGTH2 usesUCS2 code points.
     --返回以UCS2代码点为单位的长度.

LENGTH4 usesUCS4 code points.
    --返回以UCS4代码点为单位的长度.
http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions088.htm#SQLRF00658

mysql: length char_length
BIT_LENGTH() Return length of argument in bits
CHAR_LENGTH() Return number of characters in argument
CHARACTER_LENGTH() A synonym for CHAR_LENGTH()
LENGTH() Return the length of a string in bytes
http://dev.mysql.com/doc/refman/5.0/en/string-functions.html