SQL_bit_char_length1
oracle length

SELECT rpad(ename,16,'.') "rpad/name", length(rpad(ename,16,'.'))"r-length", lpad(ename,16,'.')"lpad-name", length(lpad(ename,16,'.'))"l-length" FROM emp where rownum <7

postgresql :

SELECT rpad(ename,12,'.')"rpdname", bit_length(rpad(ename,12,'.'))"bitlength", char_length(lpad(ename,12,'.'))"charlength" FROM emp limit 6

MySQL

SELECT rpad(ename,16,'.') "rpad/name", length(rpad(ename,16,'.'))"r-length", lpad(ename,16,'.')"lpad-name", length(lpad(ename,16,'.'))"l-length" FROM emp limit 6

SELECT rpad(ename,12,'.')"rpdname", bit_length(rpad(ename,12,'.'))"bitlength", char_length(lpad(ename,12,'.'))"charlength" FROM emp limit 6

BIT_LENGTH: length of the strings in bits
CHAR_LENGTH or character_length:  returns the number of characters in a string
Oracle:
 
Postgresql
MySQL

MySQL:bit_length, char_length