Alvaro Herrera <alvherre@surnet.cl> writes:
> I think this is done by AddRelationRawConstraints. You'd have to get
> the parsetree of the default expression. I think you could get that by
> applying raw_parser() to pg_attrdef.adsrc.
Not adsrc --- that's not trustworthy.
In practice I think you could just assume you know what the default
expression ought to be, and store a new one without looking at the old.
regards, tom lane