Re: varchar vs varchar(n)

Ken Benson <Ken(at)infowerks(dot)com> writes:
> On Sun, Nov 12, 2017 at 2:34 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us<mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us>> wrote:
> Generally speaking, I would only use varchar(n) when there is a clear
> reason traceable to application requirements why there has to be a
> limit, and why the limit should be n and not some other number.

> Is this true – even if the column in question will be used in (or as part of) an INDEX.
> It seems to be the index would work best if the length of the columns involved is a known value.

varchar(n) doesn't have a known length. Even char(n) doesn't have a known
length in the presence of variable-width text encodings. So there are no
optimizations of the sort you're imagining in Postgres.

regards, tom lane