Syntax:
TO_BASE64(str)

Converts the string argument to base-64 encoded form and returns the
result as a character string with the connection character set and
collation. If the argument is not a string, it is converted to a string
before conversion takes place. The result is NULL if the argument is
NULL. Base-64 encoded strings can be decoded using the FROM_BASE64()
function.

URL: http://dev.mysql.com/doc/refman/5.7/en/string-functions.html

