Re: [HACKERS] [SQL] Case Preservation disregarding case
-Original Message- From: Stephan Szabo [mailto:[EMAIL PROTECTED] 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. ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] [SQL] Case Preservation disregarding case
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: WeeklySalesSomeStrangeName ------ 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:[EMAIL PROTECTED] 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" <[EMAIL PROTECTED]> 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 IB there is exactly one corresponding case-normal form CNF. CNF is an 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 of a 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 ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] [SQL] Case Preservation disregarding case
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:[EMAIL PROTECTED] 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" <[EMAIL PROTECTED]> writes: > At Teradata, we certainly interpreted the spec to allow case-preserving, > but case-insensitive, identifiers. ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] [SQL] 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:[EMAIL PROTECTED] 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" <[EMAIL PROTECTED]> 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 and a are equivalent if the of the (with every letter that is a lower-case letter replaced by the corresponding upper-case letter or letters) and the of the (with all occurrences of replaced by and all occurrences of replaced by ), considered as the repetition of a that specifies a of SQL_IDENTIFIER and an implementation-defined collation that is sensitive to case, compare equally according to the comparison rules in Subclause 8.2, "". 27) Two s are equivalent if their s, considered as the repetition of a that specifies a of SQL_IDENTIFIER and an implementation-defined collation that is sensitive to case, compare equally according to the comparison rules in Subclause 8.2, "". 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 ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] [SQL] Case Preservation disregarding case
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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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? http://archives.postgresql.org ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
