Calculates an MD5 128-bit checksum for the string. The value is returned as a string of 32 hex digits, or NULL if the argument was NULL. The return value can, for example, be used as a hash key.
online md5 generator: http://www.md5.cz/
MySQL has md5 function: https://dev.mysql.com/doc/refman/5.5/en/encryption-functions.html#function_md5
PostgreSQL also has md5 function: http://www.postgresql.org/docs/9.1/static/functions-string.html