Re: [HACKERS] Case Preservation disregarding case

We treated quoted identifiers as case-specific, as the spec requires.

In the catalog, we stored TWO columns... The column name with case
converted as appropriate (as PostgreSQL already does), used for looking
up the attribute,
And a second column, which was the column name with the case exactly as
entered by the user.

So, your example would work just fine.

-----Original Message-----
From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Monday, October 30, 2006 10:35 PM
To: Chuck McDevitt
Cc: beau hargis; pgsql-sql(at)postgresql(dot)org; pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
sensitivity?

"Chuck McDevitt" <cmcdevitt(at)greenplum(dot)com> writes:
> At Teradata, we certainly interpreted the spec to allow
case-preserving,
> but case-insensitive, identifiers.

Really?

As I see it, the controlling parts of the SQL spec are (SQL99 sec 5.2)

26) A <regular identifier> and a <delimited identifier> are
equivalent if the <identifier body> of the <regular
identifier>
(with every letter that is a lower-case letter replaced by
the
corresponding upper-case letter or letters) and the
<delimited
identifier body> of the <delimited identifier> (with all
occurrences of <quote> replaced by <quote symbol> and all
occurrences of <doublequote symbol> replaced by <double
quote>),
considered as the repetition of a <character string literal>
that specifies a <character set specification> of
SQL_IDENTIFIER
and an implementation-defined collation that is sensitive to
case, compare equally according to the comparison rules in
Subclause 8.2, "<comparison predicate>".

27) Two <delimited identifier>s are equivalent if their
<delimited
identifier body>s, considered as the repetition of a
<character
string literal> that specifies a <character set
specification>
of SQL_IDENTIFIER and an implementation-defined collation
that is sensitive to case, compare equally according to the
comparison rules in Subclause 8.2, "<comparison predicate>".

Note well the "sensitive to case" bits there. Now consider

CREATE TABLE tab (
"foobar" int,
"FooBar" timestamp,
"FOOBAR" varchar(3)
);

We can *not* reject this as containing duplicate column names, else we
have certainly violated rule 27. Now what will you do with

SELECT fooBar FROM tab;

? The spec is unquestionably on the side of "you selected the varchar
column"; historical Postgres practice is on the side of "you selected
the int column". AFAICS a case-insensitive approach would have to
fail with some "I can't identify which column you mean" error. I am
interested to see where you find support for that in the spec...

regards, tom lane