Case Preservation disregarding case sensitivity?
Hello all.
As this is my first post to this particular mailing list, let me preface this
with a couple of items:
1) I have, indeed, searched far and wide for the answer to my question. I have
read and understood the responses to similar posts posing similar questions.
My next stop after this is the postgresql source code.
2) I develop database driven applications for telephony and mobile
applications in C/C++, perl and python. The databases I am working with
exceed 100GB. We have several production database systems.
3) I am pushing hard to replace our MySQL installations with PostgreSQL
(open-source and/or commercial) because Postgres has performed better by
several orders of magnitude and has been more stable and as consumed half the
resources in my testing.
The behavior I am seeing in Postgres in my development and migration process
is a showstopper. The manner in which Postgres handles case-sensitivity
breaks the current tools that I use and the applications that have been
written.
I am aware of the double-quote 'feature' which indicates that an element
should be treated in a case-sensitive way. This as been the 'answer' to every
question of this sort. This 'feature' does not solve the problem and
introduces other problems.
I have a data set that is designed in such a way as:
CREATE TABLE user_profile (
userProfileId int8 not null primary key,
userProfileTypeId int8 not null
);
CREATE TABLE user_profile_type (
userProfileTypeId int8 not null primary key,
userProfileType varchar not null
);
Ok, the description of the table from the database:
Table "public.user_profile"
Column | Type | Modifiers
-------------------+--------+-----------
userprofileid | bigint | not null
userprofiletypeid | bigint | not null
Indexes:
"user_profile_pkey" PRIMARY KEY, btree (userprofileid)
Ok, adding a foreign key:
ALTER table user_profile ADD CONSTRAINT fk_uproftype FOREIGN KEY
(userProfileTypeId) REFERENCES user_profile_type (userProfileTypeId);
...works successfully.
Works as it is supposed to work. Postgres is supposed to be case sensitive,
which is not a problem, but I want it to preserve the case of the column
names.
Every search has turned up the suggestion of using double-quotes around
identifiers in the creation of the tables. So we'll try that:
DROP TABLE user_profile;
DROP TABLE user_profile_type;
CREATE TABLE user_profile (
"userProfileId" int8 not null primary key,
"userProfileTypeId" int8 not null
);
CREATE TABLE user_profile_type (
"userProfileTypeId" int8 not null primary key,
"userProfileType" varchar not null
);
The table description:
Table "public.user_profile"
Column | Type | Modifiers
-------------------+--------+-----------
userProfileId | bigint | not null
userProfileTypeId | bigint | not null
Indexes:
"user_profile_pkey" PRIMARY KEY, btree ("userProfileId")
Case was preserved. Now lets add the foreign key just as we did before (note
that the case in the table definition and the ALTER TABLE query is the same):
ALTER TABLE user_profile ADD CONSTRAINT fk_uproftype FOREIGN KEY
(userProfileTypeId) REFERENCES user_profile_type (userProfileTypeId);
ERROR: column "userprofiletypeid" referenced in foreign key constraint does
not exist
The case was preserved, but the case-insensitivity only works one way. The
case of the input identifier was 'normalized' in a way, but not matched
against the column names in a case-insensitive way. This is the behavior that
breaks the tools that I use. I cannot modify these tools to add quotes around
the identifiers, and in my mind I should not have to.
OK, another query (perfectly valid SQL):
insert into user_profile_type
(userProfileTypeId,userProfileType) VALUES(1,'ABNORMAL');
ERROR: column "userprofiletypeid" of relation "user_profile_type" does not
exist
I am hoping that there is an easy way to obtain case-preservation with
case-insensitivity, or at the very least, case-preservation and complete
case-sensitivity, or case-preservation and a consistant case-conversion
strategy.
The case of the column names need to be preserved because that is the way the
schema is designed and most importantly (VERY, VERY IMPORTANT), column names
are used in apps as hash values, or as named references which are case
sensitive and as such need to be delivered to the client in exactly in the
manner specified at the time of table creation.
Again, I am looking for a way (magic, patches, whiskey, etc) that will give me
case-preservation with EITHER case-sensitivity OR case-insensitivity, but not
both as I am seeing.
Thanks in advance. I am hoping to find a solution to this so I can actually
convert one of our databases to use Postgres. And I can say that little
issues like this are precisely why Postgres was never used in this
organization before, even though several of the other database developers
like the features, stability and performance of Postgres.
At 07:23 PM 10/27/06, beau hargis wrote:
I am aware of the double-quote 'feature' which indicates that an element
should be treated in a case-sensitive way. This as been the 'answer' to every
question of this sort. This 'feature' does not solve the problem and
introduces other problems.
If you use double-quotes when creating the table, you need to use
double-quotes EVERY time you access those elements. Neither of your two
examples (that produced errors) have double quotes.
ALTER TABLE user_profile ADD CONSTRAINT fk_uproftype FOREIGN KEY
(userProfileTypeId) REFERENCES user_profile_type (userProfileTypeId);ERROR: column "userprofiletypeid" referenced in foreign key constraint does
not exist
insert into user_profile_type
(userProfileTypeId,userProfileType) VALUES(1,'ABNORMAL');ERROR: column "userprofiletypeid" of relation "user_profile_type" does not
exist
The second query should be:
insert into user_profile_type ("userProfileTypeId","userProfileType")
VALUES(1,'ABNORMAL');
Hi Beau,
On Fri, 2006-10-27 at 16:23 -0700, beau hargis wrote:
I am hoping that there is an easy way to obtain case-preservation with
case-insensitivity, or at the very least, case-preservation and complete
case-sensitivity, or case-preservation and a consistant case-conversion
strategy.The case of the column names need to be preserved because that is the way the
schema is designed and most importantly (VERY, VERY IMPORTANT), column names
are used in apps as hash values, or as named references which are case
sensitive and as such need to be delivered to the client in exactly in the
manner specified at the time of table creation.Again, I am looking for a way (magic, patches, whiskey, etc) that will give me
case-preservation with EITHER case-sensitivity OR case-insensitivity, but not
both as I am seeing.Thanks in advance. I am hoping to find a solution to this so I can actually
convert one of our databases to use Postgres. And I can say that little
issues like this are precisely why Postgres was never used in this
organization before, even though several of the other database developers
like the features, stability and performance of Postgres.
I went through the same issue in my conversion from MySQL to Postgres
and (since I had a small application) I ended up changing up all my
tables and columns "UserProfile" to user_profile.
I'm afraid however, that it's MySQL that is the odd man out. I haven't
researched this completely but I believe PG follows either the FIPS-127
or SQL-92 standard with respect to what are called "delimited
identifiers". Basically, this says if you want case sensitivity in
identifier names, you have to use double quotes wherever you refer to
the identifier. Without the double quotes, the SQL implementor can
either use UPPERCASE (as I believe Oracle and DB2 do) or lowercase (as
PG does) when it displays those identifiers.
Joe
Case was preserved. Now lets add the foreign key just as we did before (note
that the case in the table definition and the ALTER TABLE query is the same):ALTER TABLE user_profile ADD CONSTRAINT fk_uproftype FOREIGN KEY
(userProfileTypeId) REFERENCES user_profile_type (userProfileTypeId);
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^
ERROR: column "userprofiletypeid" referenced in foreign key constraint does
not exist
When ever you defince a column with quotes, all references to it must also contain quotes. Try:
ALTER TABLE user_profile ADD CONSTRAINT fk_uproftype FOREIGN KEY
("userProfileTypeId") REFERENCES user_profile_type ("userProfileTypeId");
OK, another query (perfectly valid SQL):
insert into user_profile_type
(userProfileTypeId,userProfileType) VALUES(1,'ABNORMAL');
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^
ERROR: column "userprofiletypeid" of relation "user_profile_type" does not
exist
Try:
insert into user_profile_type
("userProfileTypeId","userProfileType") VALUES(1,'ABNORMAL');
I am hoping that there is an easy way to obtain case-preservation with
case-insensitivity, or at the very least, case-preservation and complete
case-sensitivity, or case-preservation and a consistant case-conversion
strategy.Again, I am looking for a way (magic, patches, whiskey, etc) that will give me
case-preservation with EITHER case-sensitivity OR case-insensitivity, but not
both as I am seeing.
Perhaps in your queries or views you use the AS keywork to respecify the column name with
upper/lower cases.
i.e.
mydb=# select id as "Id" from foo;
Id
---------
goodbye
(1 row)
Regards,
Richard Broersma Jr.
Again, I am looking for a way (magic, patches, whiskey, etc) that will give me
case-preservation with EITHER case-sensitivity OR case-insensitivity, but not
both as I am seeing.Thanks in advance. I am hoping to find a solution to this so I can actually
convert one of our databases to use Postgres. And I can say that little
issues like this are precisely why Postgres was never used in this
organization before, even though several of the other database developers
like the features, stability and performance of Postgres.
Here is an explination from the postgresql manual:
http://www.postgresql.org/docs/8.1/interactive/sql-syntax.html#SQL-SYNTAX-IDENTIFIERS
...
Quoting an identifier also makes it case-sensitive, whereas unquoted names are always folded to
lower case. For example, the identifiers FOO, foo, and "foo" are considered the same by
PostgreSQL, but "Foo" and "FOO" are different from these three and each other. (The folding of
unquoted names to lower case in PostgreSQL is incompatible with the SQL standard, which says that
unquoted names should be folded to upper case. Thus, foo should be equivalent to "FOO" not "foo"
according to the standard. If you want to write portable applications you are advised to always
quote a particular name or never quote it.)
...
Regards,
Richard Broersma Jr.
beau hargis <beauh@bluefrogmobile.com> writes:
Considering the differences that already exist between database systems and
their varying compliance with SQL and the various extensions that have been
created, I do not consider that the preservation of case for identifiers
would violate any SQL standard.
That's not how I read the spec. It is true that we are not 100% spec
compliant, but that isn't a good argument for moving further away from
spec. Not to mention breaking backwards compatibility with our
historical behavior. The change you propose would fix your application
at the cost of breaking other people's applications. Perhaps you
should consider fixing your app instead.
regards, tom lane
Import Notes
Reply to msg id not found: 200610301928.51255.beauh@bluefrogmobile.com
On Friday 27 October 2006 19:38, Joe wrote:
Hi Beau,
On Fri, 2006-10-27 at 16:23 -0700, beau hargis wrote:
I am hoping that there is an easy way to obtain case-preservation with
case-insensitivity, or at the very least, case-preservation and complete
case-sensitivity, or case-preservation and a consistant case-conversion
strategy.The case of the column names need to be preserved because that is the way
the schema is designed and most importantly (VERY, VERY IMPORTANT),
column names are used in apps as hash values, or as named references
which are case sensitive and as such need to be delivered to the client
in exactly in the manner specified at the time of table creation.I went through the same issue in my conversion from MySQL to Postgres
and (since I had a small application) I ended up changing up all my
tables and columns "UserProfile" to user_profile.I'm afraid however, that it's MySQL that is the odd man out. I haven't
researched this completely but I believe PG follows either the FIPS-127
or SQL-92 standard with respect to what are called "delimited
identifiers". Basically, this says if you want case sensitivity in
identifier names, you have to use double quotes wherever you refer to
the identifier. Without the double quotes, the SQL implementor can
either use UPPERCASE (as I believe Oracle and DB2 do) or lowercase (as
PG does) when it displays those identifiers.Joe
Again, I am at the same point I was at when searching and searching for
information on the problem, and I am not sure what the SQL standard has to
say about it: I do not, and I dont think that anyone else who is struggling
to deal with the problem does, care about case-sensitivity. I am interested
in case preservation of column names. I do, indeed, want identifiers treated
in a case insensitive way, but I want the case PRESERVED in the table
definitions and I want that case, as preserved, to be reflected in the field
names as returned by the server to any client library that connects and
initiates a query.
Case-preservation is not the same as case-sensitivity; nor is
case-normalization the same as case-insensitivity. What PostgreSQL is doing
is converting any, and all, identifiers to a lower case and then matching
those against the identifiers (as stored in the table definition) in a
case-sensitive manner. It 'normalizes' the case of the identifiers so that it
has a common internal representation; the desires of the programmer and
database architect be damned.
Referenced specification details:
From FIPS-127:
=======================================
3. Delimited identifiers. In the previous ANSI SQL specification, it was not
possible for an application to specify identifiers with spaces or other
special symbols. Also, it was not possible to protect against future assaults
on the name space for (identifier) by additions to the (reserved word) list.
The new facility for (delimited identifier) allows a user to enclose all
identifiers in double-quotation marks, thereby ensuring that the name defined
or referenced may contain spaces or other special symbols and will not be
impacted by future additions to the (reserved word) list.
=======================================
From SQL-92/Sec. 5.2:
=======================================
10)The <identifier body> of a <regular identifier> is equivalent
to an <identifier body> in which every letter that is a lower-
case letter is replaced by the equivalent upper-case letter
or letters. This treatment includes determination of equiva-
lence, representation in the Information and Definition Schemas,
representation in the diagnostics area, and similar uses.
11)The <identifier body> of a <regular identifier> (with every
letter that is a lower-case letter replaced by the equivalent
upper-case letter or letters), treated as the repetition of
a <character string literal> that specifies a <character set
specification> of SQL_TEXT, shall not be equal, according to
the comparison rules in Subclause 8.2, "<comparison predicate>",
to any <reserved word> (with every letter that is a lower-case
letter replaced by the equivalent upper-case letter or letters),
treated as the repetition of a <character string literal> that
specifies a <character set specification> of SQL_TEXT.
12)Two <regular identifier>s are equivalent if their <identifier
body>s, considered as the repetition of a <character string
literal> that specifies a <character set specification> of
SQL_TEXT, compare equally according to the comparison rules
in Subclause 8.2, "<comparison predicate>".
13)A <regular identifier> and a <delimited identifier> are equiva-
lent if the <identifier body> of the <regular identifier> (with
every letter that is a lower-case letter replaced by the equiva-
lent 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 <dou-
blequote symbol> replaced by <double quote>), considered as
the repetition of a <character string literal> that specifies a
<character set specification> of SQL_TEXT and an implementation-
defined collation that is sensitive to case, compare equally
according to the comparison rules in Subclause 8.2, "<comparison
predicate>".
14)Two <delimited identifier>s are equivalent if their <delimited
identifier body>s (with all occurrences of <quote> replaced
by <quote symbol> and all occurrences of <doublequote symbol>
replaced by <doublequote>), considered as the repetition of a
<character string literal> that specifies a <character set spec-
ification> of SQL_TEXT and an implementation-defined collation
that is sensitive to case, compare equally according to the
comparison rules in Subclause 8.2, "<comparison predicate>".
========================================
Having installed DB2 Enterprise today and taking it for a spin, it does indeed
behave in a similar manner. However, after reading through both
specifications, it seems that DB2 follows more of the spec than PostgreSQL.
The specifications state that for purpose of comparing identifiers, both
shall be converted to upper-case. DB2 displays all identifiers in upper-case
whereas PostgreSQL displays all identifiers in lower-case. This alone would
be a deviation from the specification.
It seems, however, that the regular-identifier/delimited-identifier
distinction is for the embedding of spaces or normally invalid characters
from other character sets, not for actually creating case-sensitive
identifiers. It is only a side-effect. It does not enforce any method for the
representation of the identifiers which the client expects, either. Since a
query can be constructed which specifies aliases (... AS ...), the
presentation of the data is implementation/runtime specific.
Considering the differences that already exist between database systems and
their varying compliance with SQL and the various extensions that have been
created, I do not consider that the preservation of case for identifiers
would violate any SQL standard. The end result being eaiser migration, the
continued operation of cross-platform tools and applications, and a database
designer or data architect having more flexibility in the construction and
presentation of a database.
Again, the distinction between case-sensitivity and case-preservation, and,
case-insensitivity and case-normalization needs to be recognized. Having
case-preservation defined in the CREATE TABLE syntax and/or a server
configuration seems, to me, to be a valuable addition. Of course, making it
an option would not interfere with the current state of affairs.
I have looked through the source code and have identified places which need to
be patched to make this possible. Tomorrow I will work on that and see what
it will impact in the code. Let me know what you think.
At Teradata, we certainly interpreted the spec to allow case-preserving,
but case-insensitive, identifiers.
Users really liked it that way: If you re-created a CREATE TABLE
statement from the catalog, you could get back exactly the case the user
had entered, but people using the table didn't need to worry about case.
And column titles in reports would have the nice case preserving
information.
Sort of like how Windows systems treat file names... The case is
preserved, but you don't need to know it to access the file.
I know UNIX users usually think "case-preserving with case-insensitive"
a foreign concept, but that doesn't mean the average user feels the
same.
If I want my column named "WeeklyTotalSales", I really don't want to
have to always quote it and type in the exact case.
-----Original Message-----
From: pgsql-hackers-owner@postgresql.org
[mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Tom Lane
Sent: Monday, October 30, 2006 7:24 PM
To: beau hargis
Cc: pgsql-sql@postgresql.org; pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
sensitivity?
beau hargis <beauh@bluefrogmobile.com> writes:
Considering the differences that already exist between database
systems and
their varying compliance with SQL and the various extensions that have
been
created, I do not consider that the preservation of case for
identifiers
would violate any SQL standard.
That's not how I read the spec. It is true that we are not 100% spec
compliant, but that isn't a good argument for moving further away from
spec. Not to mention breaking backwards compatibility with our
historical behavior. The change you propose would fix your application
at the cost of breaking other people's applications. Perhaps you
should consider fixing your app instead.
regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 4: Have you searched our list archives?
"Chuck McDevitt" <cmcdevitt@greenplum.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
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@sss.pgh.pa.us]
Sent: Monday, October 30, 2006 10:35 PM
To: Chuck McDevitt
Cc: beau hargis; pgsql-sql@postgresql.org; pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
sensitivity?
"Chuck McDevitt" <cmcdevitt@greenplum.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
Oh... And Microsoft SQLServer does something similar.
At Greenplum, we've already gotten complaints from customers about this
when they were switching from MSSQL to GP's PostgreSQL-based database.
-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Monday, October 30, 2006 10:35 PM
To: Chuck McDevitt
Cc: beau hargis; pgsql-sql@postgresql.org; pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
sensitivity?
"Chuck McDevitt" <cmcdevitt@greenplum.com> writes:
At Teradata, we certainly interpreted the spec to allow
case-preserving,
Show quoted text
but case-insensitive, identifiers.
There was some discussion a couple of years ago on the -hackers list
about it, so you might like to review the archives. The consensus seemed
to be that behaviour would need to be set no later than createdb time.
The options I thought of were:
. current postgres behaviour (we need to do this for legacy reasons, of
course, as well as to keep happy the legions who hate using upper case
for anything)
. strictly spec compliant (same as current behaviour, but folding to
upper case for unquoted identifiers rather than lower)
. fully case sensitive even for unquoted identifiers (not spec compliant
at all, but nevertheless possibly attractive especially for people
migrating from MS SQLServer, where it is an option, IIRC).
To this you propose, as I understand it, to have a fourth possibility
which would be spec compliant for comparison purposes but would label
result set columns with the case preserved name originally used (or
would you use the casing used in the query?).
These could be accomplished I think with a second catalog column like
you suggest, in a number of places, but making sure all the code paths
were covered might be somewhat laborious. We could probably add the
second option without being nearly so invasive, though, and some people
might feel that that would be sufficient.
cheers
andrew
Chuck McDevitt wrote:
Show quoted text
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@sss.pgh.pa.us]
Sent: Monday, October 30, 2006 10:35 PM
To: Chuck McDevitt
Cc: beau hargis; pgsql-sql@postgresql.org; pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
sensitivity?"Chuck McDevitt" <cmcdevitt@greenplum.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 withSELECT 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...
On Tue, Oct 31, 2006 at 12:55:46PM -0500, Andrew Dunstan wrote:
To this you propose, as I understand it, to have a fourth possibility
which would be spec compliant for comparison purposes but would label
result set columns with the case preserved name originally used (or
would you use the casing used in the query?).
The big issue I see with this is that it would break PQfname on the
client end, since that's case sensetive too. Most client languages are,
so you really are between a rock and a hard place.
Making PQfname case-insensetive also screws up in Tom's example.
One way to appraoch this is to consider this a setting of the collation
of the name datatype. If a case-insensetive collation is selected at
initdb time, then Tom's example would indeed fail, but that's a choice
someone made. Problem being, you'd have to export that choice to
clients to make PQfname work, and that's going to messy.
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
Show quoted text
From each according to his ability. To each according to his ability to litigate.
On Tue, 31 Oct 2006, Chuck McDevitt wrote:
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.
Wouldn't using that second column's value tend to often violate 5.2SR10
(at least that's the reference item in SQL92)? AFAICT, that rule basically
says that the regular identifier is equivalent to the case-folded one for
purposes of information and definition schema and similar purposes which
seems like it would be intended to include things like column labeling for
output. There's a little bit of flexibility there on both similar purposes
and equivalence, though.
----
10) The <identifier body> of a <regular identifier> is equivalent
to an <identifier body> in which every letter that is a lower-
case letter is replaced by the equivalent upper-case letter
or letters. This treatment includes determination of equiva-
lence, representation in the Information and Definition Schemas,
representation in the diagnostics area, and similar uses.
-----Original Message-----
From: Stephan Szabo [mailto:sszabo@megazone.bigpanda.com]
Sent: Tuesday, October 31, 2006 10:23 AM
To: Chuck McDevitt
Cc: Tom Lane; beau hargis; pgsql-sql@postgresql.org;
pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] [SQL] Case Preservation disregarding case
On Tue, 31 Oct 2006, Chuck McDevitt wrote:
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.
Wouldn't using that second column's value tend to often violate 5.2SR10
(at least that's the reference item in SQL92)? AFAICT, that rule
basically
says that the regular identifier is equivalent to the case-folded one
for
purposes of information and definition schema and similar purposes which
seems like it would be intended to include things like column labeling
for
output. There's a little bit of flexibility there on both similar
purposes
and equivalence, though.
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.
Anyway, we have many things that are "enhancements" beyond the spec, and
this could also be considered an enhancement.
"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 as and including
determination of identifier equivalence, representation in
the Definition and Information Schemas, 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
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 (WeeklySales numeric(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 as and including
determination of identifier equivalence, representation in
the Definition and Information Schemas, 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
On Wed, 2006-11-01 at 11:31 -0500, Chuck McDevitt wrote:
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 (WeeklySales numeric(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);
This would be very good indEEd.
It can be very annoying trying to locate a table when the user swears
they called it one thing and actually the case or quotation is
different. Current behaviour isn't useful, even if it is "onspec" (or is
that OnSpec?). Would be better to make this behaviour a userset
switchable between the exactly compliant and the more intuitive.
We have namespaces to differentiate between two sources of object names,
so anybody who creates a schema where MyColumn is not the same thing as
myColumn is not following sensible rules for conceptual distance. It's
certainly an error of best practice, even if its not actually a bug.
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
----------- ---------------
...
Producing "?column?" or somesuch to use in the report, it could return a
title like "sum(WeeklySales)"
That would be just great. I'm not sure the spec says what the titles
should be, does it?
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
"Simon Riggs" <simon@2ndquadrant.com> writes:
We have namespaces to differentiate between two sources of object names,
so anybody who creates a schema where MyColumn is not the same thing as
myColumn is not following sensible rules for conceptual distance.
I'd agree that that is not a good design practice, but the fact remains
that they *are* different per spec.
Would be better to make this behaviour a userset
switchable between the exactly compliant and the more intuitive.
That's certainly not happening --- if you make any changes in the
semantics of equality of type name, it would have to be frozen no
later than initdb time, for exactly the same reasons we freeze
locale then (hint: index ordering).
regards, tom lane
beau hargis wrote:
Having installed DB2 Enterprise today and taking it for a spin, it does indeed
behave in a similar manner. However, after reading through both
specifications, it seems that DB2 follows more of the spec than PostgreSQL.
The specifications state that for purpose of comparing identifiers, both
shall be converted to upper-case. DB2 displays all identifiers in upper-case
whereas PostgreSQL displays all identifiers in lower-case. This alone would
be a deviation from the specification.
True. We lowercase because historically we have, and because
all-upper-case is hard to read.
--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
