Unbinding a default means disconnecting it from a particular column or user-defined datatype. An unbound default remains in the database and is available for future use. Use sp_unbindefault to remove the binding between a default and a column or datatype.
Here is how to unbind the current default from the city column of the friends_etc table:
execute sp_unbindefault "friends_etc.city"
To unbind a default from the user-defined datatype citytype, use:
sp_unbindefault citytype
The complete syntax of sp_unbindefault is:
sp_unbindefault objname [, futureonly]
If the objname parameter you give is not of the form table.column, SAP ASE assumes it is a user-defined datatype. When you unbind a default from a user-defined datatype, the default is unbound from all columns of that type unless you give the optional futureonly parameter, which prevents existing columns of that datatype from losing their binding with the default.