FROMBASE64
Converts a Base 64 string representation into a byte array.
Syntax
byte[]FROMBASE64(string value)
Example
FROMBASE64("Q29udmVydHMgYSBCYXNlIDY0IHN0cmluZyByZXByZXNlbnRhdGlvbiBiYWNrIGludG8gYSBCeXRlIEFycmF5")
Will return "Converts a Base 64 string representation back into a Byte Array".
You can enter you column name rather than a hardcoded value so that each row of data is processed:
FROMBASE64(MyColumn)