Re: [SQL] Case Preservation disregarding case - Mailing list pgsql-hackers

Sorry, my last mail wasn't well thought out.  Yes, the
information_schema needs the case-folded name (although it might be ok
to add additional columns to the information_schema for extra
information).

But, stepping back from all that, what is it the users want?

1)  When re-creating a CREATE TABLE statement from whatever catalog
info, they'd like the names to come back exactly as then entered them.If I do:        CREATE TABLE BobsTable
(WeeklySalesnumeric(10,2), 
"SomeStrangeName" int);
     They'd like to see exactly that when the CREATE TABLE gets
re-created, not what we do now:
   CREATE TABLE bobstable (weeklysales numeric(10,2),
"SomeStrangeName" int);

2)  When doing reports, they'd like the name as entered to be the title
of the column:    Select * from bobstable;
     Would be nice if they saw this:         WeeklySales        SomeStrangeName         -----------
---------------

For compatibility with existing apps and spec compliance, you'd still
want PQfname() to return the case-folded name.
But there isn't any reason you couldn't also return a "suggested title"
field (PQftitle?) which preserves the user's case.

You could also extend the concept of a PQftitle to make nicer titles for
expressions.  Instead of SELECT sum(WeeklySales) from BobsTable;

Producing "?column?" or somesuch to use in the report, it could return a
title like "sum(WeeklySales)"

-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Tuesday, October 31, 2006 10:38 PM
To: Chuck McDevitt
Cc: Stephan Szabo; beau hargis; pgsql-sql@postgresql.org;
pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case

"Chuck McDevitt" <cmcdevitt@greenplum.com> writes:
> Equivalent, yes.  But I can interpret that clause it mean I can show
> either the case folded or non-case-folded value in the information
> schema, as they are equivalent.

Well, that's an interesting bit of specs-lawyering, but I don't see
how you can defend it against these rules in SQL99 5.2:
       21) For every <identifier body> IB there is exactly one           corresponding case-normal form CNF. CNF is an
<identifier
body>           derived from IB as follows.
           Let n be the number of characters in IB. For i ranging from
1           (one) to n, the i-th character M(i) of IB is translated into
the           corresponding character or characters of CNF as follows.
           Case:
           a) If M(i) is a lower case character or a title case
character             for which an equivalent upper case sequence U is defined
by             Unicode, then let j be the number of characters in U; the             next j characters of CNF are U.
           b) Otherwise, the next character of CNF is M(i).
       22) The case-normal form of the <identifier body> of a <regular           identifier> is used for purposes such
asand including           determination of identifier equivalence, representation in           the Definition and
InformationSchemas, and representation 
in           diagnostics areas.
           NOTE 44 - Any lower-case letters for which there are no
upper-           case equivalents are left in their lower-case form.

Again, obviously we are not compliant because we fold to lower rather
than upper case, but I do not see how you can read (22) as not requiring
the information schema to show the upper-cased form.  The output of
functions such as PQfname() might be considered closer to diagnostics
info than information schema, but that's covered too.

But the really serious problem with what you propose is that it would
allow two table columns with names that the system considers distinct
to show as the same string in the information schema and diagnostic
outputs.  That can't be acceptable --- it's going to break any
application that does any nontrivial analysis of what it sees there,
not to mention that it violates various primary key constraints in
the information schema specification.
        regards, tom lane