Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT

Robert Haas <robertmhaas@gmail.com> writes:
> (It's also worth pointing out that the calculations we do with
> ndistinct are pretty approximations anyway.  If the difference between
> stadistinct = -1 x 10^-6 and stadistinct = -1.4^10-6 is the thing
> that's determining whether the planner is picking the correct plan on
> your 4-billion-row table,

No, it's the loss of ability to set stadistinct to -1e-9 or -1e-12 or
-1e-15 or so that is bothering me.  In a table with billions of rows
that could become important.

Or maybe not; but the real bottom line here is that it is 100% silly to
use a different representation in this column than is used in the
underlying stadistinct column.  All you accomplish by that is to impose
on the user the intersection of the accuracy/range limits of the two
different representations.
        regards, tom lane