title: Create implicit conversion rule for custom data type
body: <p>I am writing a load of SQL to output .xml files for our customers. They prefer to have "Y" or "N" in BIT columns, rather than 1 or 0. We have a lot of BIT columns all over the place and I need to write <code>CASE WHEN 1 THEN 'Y' ELSE 'N' END</code> more times than I have had hot dinners, to convert the data.</p>
  
  <p>In a sense, that's fine and I should just get on with it and stop moaning, but I couldn't help wondering... If I created a custom datatype from a CHAR(1) base, which only allowed "Y" or "N" values, could I somehow make a rule for implicit conversion so that the machine will do the conversion for me reliably - converting 1 to "Y" and 0 to "N" every time?</p>
  
  <p>I realise that there are other possibilities for achieving the same thing (using a .xsd to convert after the event to have Y/N instead of 1/0 for instance), but I'm interested in adding the custom type and the rule - is it possible and would it be sensible?</p>