Converts a string column containing Base64 using the selected Base64 decoder Decoder options: Basic: Uses "The Base64 Alphabet" as specified in Table 1 of RFC 4648 and RFC 2045 for encoding and decoding operation.The decoder rejects data that contains characters outside the base64 alphabet. URL: Uses the "URL and Filename safe Base64 Alphabet" as specified in Table 2 of RFC 4648 for encoding and decoding. The decoder rejects data that contains characters outside the base64 alphabet. 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. All line separators or other characters not found in the base64 alphabet table are ignored in decoding operation.