Re: DROP COLUMN

Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> What I asked you is what *harder to fix* means. 

> Uh, some said that having attno's like 1,2,3,5,7,8,9 with gaps would
> cause coding problems in client applications, and that was easier to
> have the numbers as 1-9 and check a flag if the column is dropped.  Why
> that is easier than having gaps, I don't understand.  I voted for the
> gaps (with negative attno's) but client coders liked the flag, so we
> went with that.

It seems to me that the problems Chris is noticing have to do with
gaps in the sequence of valid (positive) attnums.  I don't believe that
the negative-attnum approach to marking deleted columns would make those
issues any easier (or harder) to fix.  Either way you have a gap.

But since the historical convention is "negative attnum is a system
column", and deleted columns are *not* system columns, I prefer the idea
of using a separate marker for deleted columns.  AFAICT the comments
from application coders have also been that they don't want to confuse
these two concepts.
        regards, tom lane