Re: DROP COLUMN

Hiroshi Inoue wrote:
> Bruce Momjian wrote:
> > 
> > Hiroshi Inoue wrote:
> > > > Makes sense.  Of course, we could make a syscache that didn't return
> > > > system columns either.
> > > >
> > > > Actually, the original argument for negative attno's for dropped columns
> > > > was exactly for this case, that the system column check would catch
> > > > dropped columns too,
> > >
> > > > but it causes other problems that are harder to fix
> > > > so we _dropped_ the idea.
> > >
> > > What does this mean ?
> > 
> > Client programmers prefered the dropped flag rather than negative
> > attno's so we went with that.
> 
> 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.

> > > BTW would we do nothing for clients after all ?
> > 
> > Clients will now need to check that dropped flag.
> 
> Clients would have to check the flag everywhere
> pg_attribute appears. 
> Why should clients do such a thing ?

Well, good question.  They could easily skip the dropped columns if we
used negative attno's because they usually already skip system columns.
However, they prefered a specific dropped column flag and positive
attno's.  I don't know why.  They would have to explain.

From my perspective, when client coders like Dave Page and others say
they would prefer the flag to the negative attno's, I don't have to
understand.  I just take their word for it.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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