Converts a string column to Base64 using the selected encoder Encoder options: Basic: Uses "The Base64 Alphabet" as specified in Table 1 of RFC 4648 and RFC 2045 for encoding and decoding operation. The encoder does not add any line feed (line separator) character. URL: Uses the "URL and Filename safe Base64 Alphabet" as specified in Table 2 of RFC 4648 for encoding and decoding. The encoder does not add any line feed (line separator) character. MIME: Uses "The Base64 Alphabet" as specified in Table 1 of RFC 2045 for encoding and decoding operation. The encoded output must be represented in lines of no more than 76 characters each and uses a carriage return '\r' followed immediately by a linefeed '\n' as the line separator. No line separator is added to the end of the encoded output.