Craig Ringer wrote:
> showing that your issue isn't actually with DISTINCT at all, but with Pg's unwillingness to *implicitly* cast a value of explict text type to another type.
Is there a way to make values of "undefined" type pass through the SELECT DISTINCT filter (getting checked for uniqueness) but remain "undefined" if all the values supplied for the column are "undefined"? I don't know if the internal design of SELECT DISTINCT and the type system would allow for this, but if it would, it would take care of Farid's problem without introducing implicit type casts.