Re: "_" in a serach pattern

The only difference is that varchar can have a length limit, text is
always unlimited length. There's no significant performance difference
between either. For most intents and purposes, they're equal.

varchar is better than text in that limits are already built in. You can
always impose limits on text types using rules and domains, but at a
slight performance hit and having to create and maintain your own rules
and domains. If you need limits, you might consider using varchar over
text as everything is there.

I use text since I don't want to worry about overflow. Personally,
specifying a varchar(500) column to be used as a "big string" field
makes little sense to me. But, if you need a limit for a display or a
program, you probably should use varchar. Besides, if you ever need to
convert data types, any of the postgres 8.* releases make it easy.

Peter

P.S. You might want to file a bug report about your initial problem.
According to
http://www.postgresql.org/docs/8.2/static/datatype-character.html

Values of type character are physically padded with spaces to the
specified width /n/, and are stored and displayed that way. However, the
padding spaces are treated as semantically insignificant. Trailing
spaces are disregarded when comparing two values of type character, and
they will be removed when converting a character value to one of the
other string types. Note that trailing spaces /are/ semantically
significant in character varying and text values.

It should have ignored the spaces in the char field and didn't.

Peter

Jessica Richard wrote:
> Peter,
>
> thanks a lot for your reply.
>
> Could you please tell me more....
>
> What is the difference between varchar and text? what is the benefit
> of each one? and is text alway better than varchar ?--- when it comes
> to a string column...
>
> thanks
>
> */Peter Koczan <pjkoczan(at)gmail(dot)com>/* wrote:
>
> Hi, Jessica,
> > 1. How do I get rid of the nonstandard warning, but still using the
> > index search?
> You have two options.
>
> - Turn off the warnings in the postgresql.conf file. Use this with
> caution (or don't use it at all) as it does pose a potential
> threat for
> SQL injections if other options aren't properly set. Read up at
> http://www.postgresql.org/docs/8.2/static/runtime-config-compatible.html
>
> for more detail.
> - Use escape-string formatting. This is the best practice since it is
> standards-conforming and more secure. You can do it, for instance, as
> select name from table where name like 'A!_B%' escape '!';
> You can escape with most characters, and it's mostly a matter of
> personal preference.
> >
> > 2. How do I search with a wild card % in the middle of the pattern?
> > Would varchar(80) or char(80) make a difference about the wild card
> > search (% in the middle)?
> I think that postgres is seeing the trailing whitespace on the end of
> the char type and not accounting for it in the search. In this case,
> varchar or text types would make a difference since they don't do
> whitespace padding (unless you force it in). You should remember
> that if
> you plan on converting the data type, trim the extraneous whitespace
> first. However, I would switch to varchar/text so it saves some space
> and saves you these headaches, unless there's an absolute need for
> fixed-length char fields. I use text almost exclusively for string
> data
> since it's arbitrary-length, I almost never have to worry about
> overflow
> or later administration.
>
> If you don't want to convert data, you can use the rtrim() function
> (i.e. "select rtrim(name) from ...").
>
> Peter
>
> >
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